Automatic currency processing system

ABSTRACT

An apparatus for currency discrimination comprises first and second stationary scanheads, disposed on opposite sides of a bill transport path, for scanning respective first and second opposing surfaces of a bill traveling along the bill transport path and for producing respective output signals. The bill travels along the transport path in the direction of a predetermined dimension of the bill. A memory stores master characteristic patterns corresponding to associated predetermined surfaces of a plurality of denominations of genuine bills. Sampling circuitry samples the output signals associated with the respective first and second opposing surfaces of the scanned bill. A signal processor is programmed to determine which one of the first and second opposing surfaces corresponds to the associated predetermined surfaces of the plurality of denominations of genuine bills. The processor then correlates the output signal associated with the one of the first and second opposing surfaces corresponding to the associated predetermined surfaces with the master characteristic patterns to identify the denomination of the scanned bill.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/433,920,filed May 2, 1995, now abandoned, which is a continuation-in-part of thefollowing U.S. patent applications and/or U.S. patents:

Pending Ser. No. 08/399,854 filed Mar. 7, 1995;

Ser. No. 08/394,752, filed Feb. 27, 1995, now U.S. Pat. No. 5,724,438;

Pending Ser. No. 08/362,848 filed Dec. 22, 1994;

Ser. No. 08/340,031 filed Nov. 14, 1994, now U.S. Pat. No. 5,815,592;

Ser. No. 08/317,349 filed Oct. 4, 1994, now U.S. Pat. No. 5,640,463;

Ser. No. 08/287,882 filed Aug. 9, 1994, now U.S. Pat. No. 5,652,802;

Ser. No. 08/243,807 filed May 16, 1994, now U.S. Pat. No. 5,633,949;

Pending Ser. No. 08/226,660 filed Apr. 12, 1994;

Abandoned Ser. No. 08/219,093 filed on Mar. 29, 1994;

Ser. No. 08/207,592 filed Mar. 8, 1994, now U.S. Pat. No. 5,467,406;

Pending U.S. Ser. No. 08/399,854 filed Mar. 7, 1995, is acontinuation-in-part of Ser. No. 08/394,752, filed Feb. 27, 1995, nowU.S. Pat. No. 5,724,438, Ser. No. 08/340,031 (allowed on Mar. 30, 1998),now U.S. Pat. No. 5,815,592, and Ser. No. 08/287,882, filed May 16,1994, now U.S. Pat. No. 5,633,949.

U.S. Ser. No. 08/394,752, filed Feb. 27, 1995, now U.S. Pat. No.5,724,438, is a continuation-in-part of pending Ser. No. 08/340,031 andSer. No. 08/127,334 filed Sep. 27, 1993, now U.S. Pat. No. 5,467,405.

Pending U.S. Ser. No. 08/362,848 filed Dec. 22, 1994 is acontinuation-in-part of pending Ser. No. 08/340,031 (allowed Mar. 30,1998).

U.S. Ser. No. 08/340,031 filed Nov. 14, 1994 (allowed on Mar. 30, 1998),now U.S. Pat. No. 5,815,592, is a continuation-in-part of Ser. No.08/243,807, now U.S. Pat. No. 5,633,949, and Ser. No. 08/207,592, nowU.S. Pat. No. 5,467,406.

Ser. No. 08/287,882 filed Aug. 9, 1994, now U.S. Pat. No. 5,652,802, isa continuation-in-part of Ser. No. 08/207,592, now U.S. Pat. No.5,467,406, Ser. No. 08/219,093, now abandoned, and Ser. No. 08/127,334filed Sep. 27, 1993, now U.S. Pat. No. 5,467,405.

U.S. patent application Ser. No. 08/243,807 filed May 16, 1994, now U.S.Pat. No. 5,633,949, is a continuation-in-part of abandoned Ser. No.08/219,093, and Ser. No. 08/127,334, now U.S. Pat. No. 5,467,405.

Pending U.S. patent application Ser. No. 08/226,660, filed Apr. 12,1994, is a continuation-in-part of Ser. No. 08/127,334, now U.S. Pat.No. 5,467,405.

Abandoned U.S. patent application Ser. No. 08/219,093 filed on Mar. 29,1994, is a continuation-in-part of Ser. No. 08/127,334, now U.S. Pat.No. 5,467,405.

U.S. Ser. No. 08/207,592 filed Mar. 8, 1994, now U.S. Pat. No.5,467,406, is a continuation-in-part of Ser. No. 08/127,334, now U.S.Pat. No. 5,467,405.

U.S. Ser. No. 08/127,334, filed Sep. 27, 1993, now U.S. Pat. No.5,467,405, is a continuation of Ser. No. 07/885,648, filed on May 19,1992, now U.S. Pat. No. 5,295,196, which is a continuation-in-part ofabandoned U.S. patent application Ser. No. 07/475,111, filed Feb. 5,1990.

Ser. No. 08/201,350 filed Feb. 24, 1994, now U.S. Pat. No. 5,542,880, isa continuation-in-part of Ser. No. 08/149,660, filed Nov. 9, 1993, nowU.S. Pat. No. 5,507,379, which is in turn a continuation-in-part of Ser.No. 08/115,319, filed Sep. 1, 1993, now U.S. Pat. No. 5,429,550, whichis in turn a continuation-in-part of Ser. No. 07/951,731, filedSeptember 25, now U.S. Pat. No. 5,299,977, which is in turn acontinuation-in-part of Ser. No. 07/904,161 filed Aug. 21, 1992, nowU.S. Pat. No. 5,277,651, which in turn is a continuation of Ser. No.07/524,134 filed May 14, 1990, now U.S. Pat. No. 5,141,443.

Ser. No. 08/399,771 filed Mar. 7, 1995, now U.S. Pat. No. 5,630,494.

FIELD OF THE INVENTION

The present invention relates to currency processing systems such asautomatic teller machines and currency redemption machines.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide an improvedautomatic teller machine ("ATM") or currency redemption machine that iscapable of processing cash deposits as well as withdrawals.

Another object of this invention is to provide such machines that arecapable of accepting and dispensing coins as well as bills.

A further object of this invention is to provide such machines thatautomatically evaluate the authenticity, as well as the denomination, ofthe cash that is deposited, whether in the form of bills or coins.

Still another object of the invention is to provide such machines thatare coupled to the cash accounting system of a bank or other financialinstitution so that the customer's account can be immediately creditedwith verified cash deposit amounts.

In accordance with the present invention, the foregoing objectives arerealized by providing a currency processing machine for receiving anddispensing cash and substantially immediately furnishing an associatedcash accounting system with data, including the value of the currencyprocessed, for each transaction. The machine includes a bill dispenserhaving a bill storage device and controllable transport means fordispensing selected numbers of bills from the storage device, a billreceptacle for receiving stacks of bills to be deposited, and a billcounter and scanner for rapidly removing the bills one at a time fromthe receptacle and counting the bills while determining the denominationof each bill. The counter and scanner also generates data representingthe denomination of each bill, and the number of bills of eachdenomination, passed through the counter and scanner. A memory receivesand stores data representing the number of bills of each denominationpassed through the counter and scanner in each transaction, and datarepresenting the total value of the bills passed through the counter andscanner in each transaction. A control system transfers data from thememory to an associated cash accounting system so that the deposits andwithdrawals executed at the currency processing machine are entered inthe accounting system substantially immediately after the execution ofthose transactions. The preferred control system checks the genuinenessof each bill and coin that is counted, and produces a control signal inresponse to the detection of a non-genuine bill or coin. The processingof the bill or coin detected to be non-genuine is altered in response tosuch control signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a perspective view of an automatic teller machine embodyingthe present invention;

FIG. 1b is a diagrammatic side elevation of the machine of FIG. 1a;

FIG. 1c is a more detailed diagrammatic side elevation of the machine ofFIG. 1a;

FIG. 1d is a flow chart illustrating the sequential procedure involvedin the execution of a transaction in the machine of FIG. 1a;

FIG. 1e is a flow chart illustrating the sequential procedure involvedin the execution of a deposit of bills in the machine of FIG. 1a;

FIG. 1f is a flow chart illustrating an alternative sequential procedureinvolved in the execution of a deposit of bills in the machine of FIG.1a;

FIG. 2a is a functional block diagram of the currency scanning andcounting subassembly in the machine of FIG. 1, including a scanheadarranged on each side of a transport path;

FIG. 2b is a functional block diagram of a currency scanning andcounting device that includes a scanhead arranged on a single side of atransport path;

FIG. 2c is a functional block diagram of a currency scanning andcounting machine similar to that of FIG. 2b, but adapted to feed andscan bills along their wide dimension;

FIG. 2d is a functional block diagram of a currency scanning andcounting device similar to those of FIGS. 2a-2c but including a secondtype of scanhead for detecting a second characteristic of the currency;

FIG. 3 is a diagrammatic perspective illustration of the successiveareas scanned during the traversing movement of a single bill across anoptical sensor according to a preferred embodiment of the primaryscanhead;

FIGS. 4a and 4b are perspective views of a bill and a preferred area tobe optically scanned on the bill;

FIGS. 5a and 5b are diagrammatic side elevation views of the preferredareas to be optically scanned on a bill according to a preferredembodiment of the invention;

FIG. 6a is a perspective view of a bill showing the preferred area of afirst surface to be scanned by one of the two scanheads employed in thepreferred embodiment of the present invention;

FIG. 6b is another perspective view of the bill in FIG. 6a showing thepreferred area of a second surface to be scanned by the other of thescanheads employed in the preferred embodiment of the present invention;

FIG. 6c is a side elevation showing the first surface of a bill scannedby an upper scanhead and the second surface of the bill scanned by alower scanhead;

FIG. 6d is a side elevation showing the first surface of a bill scannedby a lower scanhead and the second surface of the bill scanned by anupper scanhead;

FIGS. 7a and 7b form a block diagram illustrating a preferred circuitarrangement for processing and correlating reflectance data according tothe optical sensing and counting technique of this invention;

FIGS. 8a and 8b comprise a flowchart illustrating the sequence ofoperations involved in implementing a discrimination and authenticationsystem according to a preferred embodiment of the present invention;

FIG. 9 is a flow chart illustrating the sequential procedure involved indetecting the presence of a bill adjacent the lower scanhead and theborderline on the side of the bill adjacent to the lower scanhead;

FIG. 10 is a flow chart illustrating the sequential procedure involvedin detecting the presence of a bill adjacent the upper scanhead and theborderline on the side of the bill adjacent to the upper scanhead;

FIG. 11a is a flow chart illustrating the sequential procedure involvedin the analog-to-digital conversion routine associated with the lowerscanhead;

FIG. 11b is a flow chart illustrating the sequential procedure involvedin the analog-to-digital conversion routine associated with the upperscanhead;

FIG. 12 is a flow chart illustrating the sequential procedure involvedin determining which scanhead is scanning the green side of a U.S.currency bill;

FIG. 13 is a flow chart illustrating the sequence of operations involvedin determining the bill denomination from the correlation results;

FIG. 14 is a flow chart illustrating the sequential procedure involvedin decelerating and stopping the bill transport system in the event ofan error;

FIG. 15a is a graphical illustration of representative characteristicpatterns generated by narrow dimension optical scanning of a $1 currencybill in the forward direction;

FIG. 15b is a graphical illustration of representative characteristicpatterns generated by narrow dimension optical scanning of a $2 currencybill in the reverse direction;

FIG. 15c is a graphical illustration of representative characteristicpatterns generated by narrow dimension optical scanning of a $100currency bill in the forward direction;

FIG. 15d is a graph illustrating component patterns generated byscanning old and new $20 bills according a second method according to apreferred embodiment of the present invention;

FIG. 15e is a graph illustrating an pattern for a $20 bill scanned inthe forward direction derived by averaging the patterns of FIG. 15daccording a second method according to a preferred embodiment of thepresent invention;

FIGS. 16a-16e are graphical illustrations of the effect produced oncorrelation pattern by using the progressive shifting technique,according to an embodiment of this invention;

FIGS. 17a-17c are a flowchart illustrating a preferred embodiment of amodified pattern generation method according to the present invention;

FIG. 18a is a flow chart illustrating the sequential procedure involvedin the execution of multiple correlations of the scan data from a singlebill;

FIG. 18b is a flow chart illustrating a modified sequential procedure ofthat of FIG. 18a;

FIG. 19a is a flow chart illustrating the sequence of operationsinvolved in determining the bill denomination from the correlationresults using data retrieved from the green side of U.S. bills accordingto one preferred embodiment of the present invention;

FIGS. 19b and 19c are a flow chart illustrating the sequence ofoperations involved in determining the bill denomination from thecorrelation results using data retrieved from the black side of U.S.bills;

FIG. 20a is an enlarged vertical section taken approximately through thecenter of the machine, but showing the various transport rolls in sideelevation;

FIG. 20b is a top plan view of the interior mechanism of the machine ofFIG. 1 for transporting bills across the optical scanheads, and alsoshowing the stacking wheels at the front of the machine;

FIG. 21a is an enlarged perspective view of the bill transport mechanismwhich receives bills from the stripping wheels in the machine of FIG. 1;

FIG. 21b is a cross-sectional view of the bill transport mechanismdepicted in FIG. 21 along line 21b;

FIG. 22 is a side elevation of the machine of FIG. 1, with the sidepanel of the housing removed;

FIG. 23 is an enlarged bottom plan view of the lower support member inthe machine of FIG. 1 and the passive transport rolls mounted on thatmember;

FIG. 24 is a sectional view taken across the center of the bottomsupport member of FIG. 23 across the narrow dimension thereof;

FIG. 25 is an end elevation of the upper support member which includesthe upper scanhead in the machine of FIG. 1, and the sectional view ofthe lower support member mounted beneath the upper support member;

FIG. 26 is a section taken through the centers of both the upper andlower support members, along the long dimension of the lower supportmember shown in FIG. 23;

FIG. 27 is a top plan view of the upper support member which includesthe upper scanhead;

FIG. 28 is a bottom plan view of the upper support member which includesthe upper scanhead;

FIG. 29 is an illustration of the light distribution produced about oneof the optical scanheads;

FIGS. 30a and 30b are diagrammatic illustrations of the location of twoauxiliary photo sensors relative to a bill passed thereover by thetransport and scanning mechanism shown in FIGS. 20a-28;

FIG. 31 is a flow chart illustrating the sequential procedure involvedin a ramp-up routine for increasing the transport speed of the billtransport mechanism from zero to top speed;

FIG. 32 is a flow chart illustrating the sequential procedure involvedin a ramp-to-slow-speed routine for decreasing the transport speed ofthe bill transport mechanism from top speed to slow speed;

FIG. 33 is a flow chart illustrating the sequential procedure involvedin a ramp-to-zero-speed routine for decreasing the transport speed ofthe bill transport mechanism to zero;

FIG. 34 is a flow chart illustrating the sequential procedure involvedin a pause-after-ramp routine for delaying the feedback loop while thebill transport mechanism changes speeds;

FIG. 35 is a flow chart illustrating the sequential procedure involvedin a feedback loop routine for monitoring and stabilizing the transportspeed of the bill transport mechanism;

FIG. 36 is a flow chart illustrating the sequential procedure involvedin a doubles detection routine for detecting overlapped bills;

FIG. 37 is a flow chart illustrating the sequential procedure involvedin a routine for detecting sample data representing dark blemishes on abill;

FIG. 38 is a flow chart illustrating the sequential procedure involvedin a routine for maintaining a desired readhead voltage level;

FIG. 39 is a top view of a bill and size determining sensors accordingto a preferred embodiment of the present invention;

FIG. 40 is a top view of a bill illustrating multiple areas to beoptically scanned on a bill according to a preferred embodiment of thepresent invention;

FIG. 41a is a graph illustrating a scanned pattern which is offset froma corresponding master pattern;

FIG. 41b is a graph illustrating the same patterns of FIG. 41a after thescanned pattern is shifted relative to the master pattern;

FIG. 42 is a side elevation of a multiple scanhead arrangement accordingto a preferred embodiment of the present invention;

FIG. 43 is a side elevation of a multiple scanhead arrangement accordingto another preferred embodiment of the present invention;

FIG. 44 is a side elevation of a multiple scanhead arrangement accordingto another preferred embodiment of the present invention;

FIG. 45 is a side elevation of a multiple scanhead arrangement accordingto another preferred embodiment of the present invention;

FIG. 46 is a top view of a staggered scanhead arrangement according to apreferred embodiment of the present invention;

FIG. 47a is a top view of a linear array scanhead according to apreferred embodiment of the present invention illustrating a bill beingfed in a centered fashion;

FIG. 47b is a side view of a linear array scanhead according to apreferred embodiment of the present invention illustrating a bill beingfed in a centered fashion;

FIG. 48 is a top view of a linear array scanhead according to anotherpreferred embodiment of the present invention illustrating a bill beingfed in a non-centered fashion;

FIG. 49 is a top view of a linear array scanhead according to anotherpreferred embodiment of the present invention illustrating a bill beingfed in a skewed fashion;

FIGS. 50a and 50b are a flowchart of the operation of a currencydiscrimination system according to a preferred embodiment of the presentinvention;

FIG. 51 is a top view of a triple scanhead arrangement utilized in adiscriminating device able to discriminate both Canadian and Germanbills according to a preferred embodiment of the present invention;

FIG. 52 is a top view of Canadian bill illustrating the areas scanned bythe triple scanhead arrangement of FIG. 51 according to a preferredembodiment of the present invention;

FIG. 53 is a flowchart of the threshold tests utilized in calling thedenomination of a Canadian bill according to a preferred embodiment ofthe present invention;

FIG. 54a illustrates the general areas scanned in generating master 10DM German patterns according to a preferred embodiment of the presentinvention;

FIG. 54b illustrates the general areas scanned in generating master 20DM, 50 DM, and 100 DM German patterns according to a preferredembodiment of the present invention;

FIG. 55 is a flowchart of the threshold tests utilized in calling thedenomination of a German bill;

FIG. 56 is a functional block diagram illustrating a first embodiment ofa document authenticator and discriminator;

FIG. 57 is a functional block diagram illustrating a second embodimentof a document authenticator and discriminator;

FIG. 58a is a side view of a document authenticating system utilizingultraviolet light;

FIG. 58b is a top view of the system of FIG. 58a along the direction58b;

FIG. 58c is a top view of the system of FIG. 58a along the direction58c; and

FIG. 59 is a functional block diagram of the optical and electroniccomponents of the document authenticating system of FIGS. 58a-58c.

FIG. 60 is perspective view of a disc-type coin sorter embodying thepresent invention, with a top portion thereof broken away to showinternal structure;

FIG. 61 is an enlarged horizontal section taken generally along line61--61 in FIG. 60;

FIG. 62 is an enlarged section taken generally along line 62--62 in FIG.61, showing the coins in full elevation;

FIG. 63 is an enlarged section taken generally along line 63--63 in FIG.61, showing in full elevation a nickel registered with an ejectionrecess;

FIG. 64 is a diagrammatic cross-section of a coin and an improved coindiscrimination sensor embodying the invention;

FIG. 65 is a schematic circuit diagram of the coin discrimination sensorof FIG. 64;

FIG. 66 is a diagrammatic perspective view of the coils in the coindiscrimination sensor of FIG. 64;

FIG. 67a is a circuit diagram of a detector circuit for use with thediscrimination sensor of this invention;

FIG. 67b is a waveform diagram of the input signals supplied to thecircuit of FIG. 67a;

FIG. 68 is a perspective view of an outboard shunting device embodyingthe present invention;

FIG. 69 is a section taken generally along line 69--69 in FIG. 68;

FIG. 70 is a section taken generally along line 70--70 in FIG. 68,showing a movable partition in a nondiverting position; and

FIG. 71 is the same section illustrated in FIG. 70, showing the movableportion in a diverting position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that it is not intended to limit theinvention to the particular forms disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

Turning now to the drawings and referring first to FIGS. 1a, 1b and 1c,there is shown an automatic teller machine ("ATM") having a bill depositreceptacle 1 as well as a bill withdrawal or return slot 2. The ATM hasthe conventional slot 3 for receiving the customer's identification cardso that the data on the card can be automatically read by a card reader.A video display 4 provides the customer with a menu of options, and alsoprompts the customer to carry out the various actions required toexecute a transaction, including the use of a keypad 5.

The illustrative ATM also has a coin deposit receptacle 6 and a coinreturn pocket 7. The deposit receptacles 1 and 6 are normally retractedwithin the machine but are advanced to their open positions (shown inFIG. 1a) when a customer initiates a transaction and selects a "cashdeposit" mode of operation. Bills and coins can then be deposited by thecustomer into the deposit receptacles 1 and 6, respectively.

After the customer has placed a stack of bills into the receptacle 1,the customer is prompted to push that receptacle into the machine, toits retracted position. This inward movement of the receptacle 1positions the stack of bills at the feed station of a bill scanning andcounting module 8 which automatically feeds, counts, scans andauthenticates the bills one at a time at a high speed (e.g., at least350 bills per minute). The bills that are recognized by the scanningmodule 8 are delivered to a conventional currency canister 9 (FIG. 1c)which is periodically removed from the machine and replaced with anempty canister. When a bill cannot be recognized by the scanning module,a diverter 10 is actuated to divert the unidentified bill to the returnslot 2 so that it can be removed from the machine by the customer.Alternatively, unrecognizable bills can be diverted to a separatecurrency canister rather than being returned to the customer. Bills thatare detected to be counterfeit are treated in the same manner asunrecognizable bills.

Though not shown in FIGS. 1a-1c, the bill transport system may alsoinclude an escrow holding area where the bills being processed in apending deposit transaction are held until the transaction is complete.Then if the declared balance entered by the customer does not agree withthe amount verified by the machine, the entire stack of bills can bereturned to the customer. If desired, this decision can be controlled bythe customer via the keypad.

When coins are deposited by the customer in the receptacle 6, thecustomer again is prompted to push that receptacle into the machine.This causes the coins to be fed by gravity into the receiving hopper ofa coin-sorting and counting module 11 which physically separates thecoins by size (denomination) while separately counting the number ofcoins of each denomination in each separate transaction. The module 11also includes a coin discriminator which detects coins that arecounterfeit or otherwise non-genuine. These unacceptable coins aredischarged from the sorter at a common exit, and the coins from thatexit are guided by a tube 12 to the coin return slot 7.

The ATM also preferably includes a conventional loose currencydispensing module 13 for dispensing loose bills, and/or a strappedcurrency dispensing module 14 for dispensing strapped currency, into areceptacle 15 at the front of the machine, in response to a withdrawaltransaction. If desired, a loose coin dispensing module 16 and/or arolled coin dispensing module 17, may also be included for dispensingcoins via the coin return pocket 7. Additional modules that may beincluded in the ATM or a redemption machine using the same system aremodules for verifying and accepting checks, food stamps, tokens and/ortickets containing bar codes.

As will be described in more detail below, each of the modules 8 and 11accumulates data representing both the number and the value of eachseparate currency item processed by these modules in each separatetransaction. At the end of each transaction, this data and the accountnumber for the transaction are downloaded to an associated cashaccounting system by a modem link, so that the customer's account can beimmediately adjusted to reflect both the deposits and the withdrawalseffected by the current transaction. Alternatively, the data from thecurrency-processing modules and the card reader can be temporarilystored within a temporary memory within the ATM, so that the data can bedownloaded at intervals controlled by the computing system on which thecash accounting system is run.

FIG. 1d is a flow chart of a subroutine for transferring data from theATM to the cash accounting system. This subroutine is entered at step10a each time a customer inserts an identification card into the ATM.The customer's account number is stored at step 10b, and step 10c theninitiates a transaction by prompting the customer to select from a menuof available deposit or withdrawal transactions, and step 10d thenmonitors the ATM system to determine when the transaction is complete.When the answer is affirmative, the bill deposit amount B_(d), the billwithdrawal amount B_(w), the coin deposit amount C_(d), and the coinwithdrawal amount Cw are stored at steps 10e, 10f, 10g and 10h, and thendownloaded to the cash accounting system at step 10i. If desired, theseamounts may be loaded into a buffer memory for later retrieval by thecomputer that controls the cash accounting system. The cash accountingsystem then enters these amounts in the customer's account, andimmediately adjusts the balance in that account accordingly.

A subroutine for executing a cash deposit of bills is shown in FIG. 1e.When this type of transaction is selected by the customer, the videodisplay prompts the customer to place the stack of bills being depositedinto the receptacle 1 and to push that receptacle into the machine. Thebill counting and scanning module then automatically withdraws one billat a time from the bottom of the stack, and scans each bill fordenomination and authentication.

Each successive bill that is withdrawn from the deposit stack is scannedat step 11a to determine the denomination of the bill, and checked forauthentication at step 11b. The results of the authentication arechecked at step 11c. If the bill cannot be authenticated, it is acounterfeit suspect and thus step 11c produces an affirmative answer.This advances the system to step 11d, which determines whether the ownerof the ATM or redemption machine has opted to return counterfeit-suspectbills to the customer. If this option has been selected, the suspectbill is returned to the customer at step 11e. If the return option hasnot been selected at step 11d, the resulting negative response advancesthe system to step 11f which transports the bill to a suspect billcanister.

If the bill is not a counterfeit suspect, the resulting negative answerat step 11c advances the system to step 11g to check the results of thescanning step. This step determines whether the bill is a "no call,"i.e., whether it was impossible for the scanning operation to determinethe denomination of the bill. If the bill is a "no call," step 11gproduces an affirmative answer, and step 11h determines whether theoption to return "no calls" to the customer has been selected. If theanswer is affirmative, the "no call" bill is returned to the customer atstep 11e. If the answer is negative, the "no call" bill is transportedto a "no call" canister at step 11i.

If the denomination of the bill has been determined by the scanner, theresulting negative response at step 11g causes the counter for thatparticular denomination to be incremented at step 11j. The dollar valueof that denomination is then added to the verified deposit amount atstep 11k to maintain a current cumulative total of the currency depositthat is being processed. The bill is then transported to an escrowholding area for the current deposit, at step 11l.

To determine when the processing of a deposit has been completed, step11m determines when the last bill in a deposited stack of bills has beencounted. When this step produces an affirmative answer, step 11m thendetermines whether the final verified deposit amount agrees with thedeclared balance that was entered by the customer through the key pad.If the answer is affirmative, the deposited bills are transported fromthe escrow holding area to a verified deposit canister at step 11o. Anegative answer at step 11n advances the system to step 11p where againthe system determines whether a "return" option has been selected. Thisoption may be preselected by the owner of the ATM or redemption machine,or it may be an option that is available to the customer. In any event,if the option has been selected, the bills are returned to the customerat step 11q to enable the customer to determine why the verified depositamount does not agree with the customer's declared balance. At thistime, the verified deposit amount is displayed to the customer alongwith an appropriate message. A negative response at step 11p causes thebills to be transported from the escrow holding area to a disputedbalance canister at step 11r.

FIG. 1f illustrates a modification of the routine of FIG. 1e whichpermits the use of a single storage canister for all of the bills,regardless of whether they are verified bills, no calls, or counterfeitsuspects. In this system the various bills are identified within thesingle canister by placing different colored markers on top of differentbills. These markers are inserted into the bill transport path so thatthey follow the respective bills to be marked into the canister.Specifically, a first marker, e.g., a marker of a first color, isinserted at step 11s following an affirmative response at step 11c and anegative response at step 11d to indicate that the bill is a counterfeitsuspect that is not to be returned to the customer. A second type ofmarker, e.g., a marker of a second color, is inserted at step 11t inresponse to an affirmative response at step 11g and a negative answer atstep 11h, to indicate that the marked bill is a counterfeit suspect. Athird type of marker, e.g., of a third color, is inserted at step 11u inresponse to negative answers at steps 11n and 11p, to indicate that themarked batch of bills represents a deposit whose verified amount did notagree with the customer's declared balance. Because this third type ofmarker identifies a batch of bills instead of a single bill, it isnecessary to insert a marker at both the beginning and end of the markedbatch.

In the event that the customer wishes to deposit "no call" bills thatare returned to the customer, the customer may key in the value andnumber of such bills and deposit them in an envelope for laterverification by the bank. A message on the display screen may advise thecustomer of this option. For example, if four $10 bills are returned,and then re-deposited by the customer in an envelope, the customer maypress a "$10" key four times. The customer then receives immediatecredit for all the bills denominated and authenticated by the scanner.Credit for the re-deposited "no call" bills is given only after the bankpicks up the deposit envelope and manually verifies the amount.Alternatively, at least preferred customers can be given full creditimmediately, subject to later verification, or immediate credit can begiven up to a certain dollar limit. In the case of counterfeit billsthat are not returned to the customer, the customer can be notified ofthe detection of a counterfeit suspect at the ATM or later by a writtennotice or personal call, depending upon the preferences of the financialinstitution.

The ATM or redemption machine may also have a "verify mode" in which itsimply denominates and totals all the currency (bills and/or coins)deposited by the customer and returns it all to the customer. If thecustomer agrees with the amount and wishes to proceed with an actualdeposit, the customer selects the "deposit mode" and re-deposits thesame batch of currency in the machine. Alternatively, the "verify mode"may hold the initially deposited currency in an escrow area until thecustomer decides whether to proceed with an actual deposit.

In the event that the machine jams or otherwise malfunctions whilecurrency is being processed, the message display screen advises thecustomer of the number and value of the currency items processed priorto the jam. The customer is instructed to retrieve the currency not yetprocessed and to manually deposit it in a sealed envelope which is thendeposited into the machine for subsequent verification. The machinemalfunction is automatically reported via modem to the home office.

Referring now to FIG. 2a, there is shown a preferred embodiment of acurrency scanning and counting module 8. The module 8 includes a billaccepting station 12 for receiving stacks of currency bills from thedeposit receptacle 1. A feed mechanism functions to pick out or separateone bill at a time for transfer to a bill transport mechanism 16 (FIG.2a) which transports each bill along a precisely predetermined transportpath, between a pair of scanheads 18a, 18b where the denomination of thebill is identified. In the preferred embodiment, bills are scanned andidentified at a rate in excess of 350 bills per minute. In the preferredembodiment depicted, each scanhead 18a, 18b is an optical scanhead thatscans for characteristic information from a scanned bill 17 which isused to identify the denomination of the bill. The scanned bill 17 isthen transported to a cassette or bill stacking station 20 where billsso processed are stacked for subsequent removal.

Each optical scanhead 18a, 18b preferably comprises a pair of lightsources 22 directing light onto the bill transport path so as toilluminate a substantially rectangular light strip 24 upon a currencybill 17 positioned on the transport path adjacent the scanhead 18. Lightreflected off the illuminated strip 24 is sensed by a photodetector 26positioned between the two light sources. The analog output of thephotodetector 26 is converted into a digital signal by means of ananalog-to-digital (ADC) convertor unit 28 whose output is fed as adigital input to a central processing unit (CPU) 30.

While the scanheads 18a, 18b of FIG. 2a are optical scanheads, it shouldbe understood that the scanheads and the signal processing system may bedesigned to detect a variety of characteristic information from currencybills. Additionally, the scanheads may employ a variety of detectionmeans such as magnetic, optical, electrical conductivity, and capacitivesensors. Use of such sensors is discussed in more detail below (see,e.g., FIG. 2d).

Referring again to FIG. 2a, the bill transport path is defined in such away that the transport mechanism 16 moves currency bills with the narrowdimension of the bills being parallel to the transport path and the scandirection. Alternatively, the system may be designed to scan bills alongtheir long dimension or along a skewed dimension. As a bill 17 traversesthe scanheads 18a, 18b, the coherent light strip 24 effectively scansthe bill across the narrow dimension of the bill. In the preferredembodiment depicted, the transport path is so arranged that a currencybill 17 is scanned across a central section of the bill along its narrowdimension, as shown in FIG. 2a. Each scanhead functions to detect lightreflected from the bill as it moves across the illuminated light strip24 and to provide an analog representation of the variation in reflectedlight, which, in turn, represents the variation in the dark and lightcontent of the printed pattern or indicia on the surface of the bill.This variation in light reflected from the narrow-dimension scanning ofthe bills serves as a measure for distinguishing, with a high degree ofconfidence, among a plurality of currency denominations which the systemis programmed to handle.

A series of such detected reflectance signals are obtained across thenarrow dimension of the bill, or across a selected segment thereof, andthe resulting analog signals are digitized under control of the CPU 30to yield a fixed number of digital reflectance data samples. The datasamples are then subjected to a normalizing routine for processing thesampled data for improved correlation and for smoothing out variationsdue to "contrast" fluctuations in the printed pattern existing on thebill surface. The normalized reflectance data represents acharacteristic pattern that is unique for a given bill denomination andprovides sufficient distinguishing features among characteristicpatterns for different currency denominations.

In order to ensure strict correspondence between reflectance samplesobtained by narrow dimension scanning of successive bills, thereflectance sampling process is preferably controlled through the CPU 30by means of an optical encoder 32 which is linked to the bill transportmechanism 16 and precisely tracks the physical movement of the bill 17between the scanheads 18a, 18b. More specifically, the optical encoder32 is linked to the rotary motion of the drive motor which generates themovement imparted to the bill along the transport path. In addition, themechanics of the feed mechanism ensure that positive contact ismaintained between the bill and the transport path, particularly whenthe bill is being scanned by the scanheads. Under these conditions, theoptical encoder 32 is capable of precisely tracking the movement of thebill 17 relative to the light strips 24 generated by the scanheads 18a,18b by monitoring the rotary motion of the drive motor.

The outputs of the photodetectors 26 are monitored by the CPU 30 toinitially detect the presence of the bill adjacent the scanheads and,subsequently, to detect the starting point of the printed pattern on thebill, as represented by the thin borderline 17a which typically enclosesthe printed indicia on U.S. currency bills. Once the borderline 17a hasbeen detected, the optical encoder 32 is used to control the timing andnumber of reflectance samples that are obtained from the outputs of thephotodetectors 26 as the bill 17 moves across the scanheads.

FIG. 2b illustrates a modified currency scanning and counting devicesimilar to that of FIG. 2a but having a scanhead on only a single sideof the transport path.

FIG. 2c illustrates another modified currency scanning and countingdevice similar to that of FIG. 2b but illustrating feeding and scanningof bills along their wide direction.

As illustrated in FIGS. 2b-2c, the transport mechanism 16 moves currencybills with a preselected one of their two dimensions (narrow or wide)being parallel to the transport path and the scan direction. FIGS. 2band 4a illustrate bills oriented with their narrow dimension "W"parallel to the direction of movement and scanning, while FIGS. 2c and4b illustrate bills oriented with their wide dimension "L" parallel tothe direction of movement and scanning.

Referring now to FIG. 2d, there is shown a functional block diagramillustrating a preferred embodiment of a currency discriminating andauthenticating system. The operation of the system of FIG. 2d is thesame as that of FIG. 2a except as modified below. The system includes abill accepting station 12 where stacks of currency bills that need to beidentified, authenticated, and counted are positioned. Accepted billsare acted upon by a bill separating station 14 which functions to pickout or separate one bill at a time for transfer to a bill transportmechanism 16 which transports each bill along a precisely predeterminedtransport path, across two scanheads 18 and 39 where the currencydenomination of the bill is identified and the genuineness of the billis authenticated. In the preferred embodiment depicted, scanhead 18 isan optical scanhead that scans for a first type of characteristicinformation from a scanned bill 17 which is used to identify the bill'sdenomination. A second scanhead 39 scans for a second type ofcharacteristic information from the scanned bill 17. While theillustrated scanheads 18 and 39 are separate and distinct, they may beincorporated into a single scanhead. For example, where the firstcharacteristic sensed is intensity of reflected light and the secondcharacteristic sensed is color, a single optical scanhead having aplurality of detectors, one or more without filters and one or more withcolored filters, may be employed (U.S. Pat. No. 4,992,860 incorporatedherein by reference). The scanned bill is then transported to a billstacking station 20 where bills so processed are stacked for subsequentremoval.

The optical scanhead 18 of the embodiment depicted in FIG. 2d comprisesat least one light source 22 directing a beam of coherent lightdownwardly onto the bill transport path so as to illuminate asubstantially rectangular light strip 24 upon a currency bill 17positioned on the transport path below the scanhead 18. Light reflectedoff the illuminated strip 24 is sensed by a photodetector 26 positioneddirectly above the strip. The analog output of photodetector 26 isconverted into a digital signal by means of an analog-to-digital (ADC)convertor unit 28 whose output is fed as a digital input to a centralprocessing unit (CPU) 30.

The second scanhead 39 comprises at least one detector 41 for sensing asecond type of characteristic information from a bill. The analog outputof the detector 41 is converted into a digital signal by means of asecond analog-to-digital converter 43 whose output is also fed as adigital input to the central processing unit (CPU) 30.

While the scanhead 18 in the embodiment of FIG. 2d is an opticalscanhead, it should be understood that the first and second scanheads 18and 39 may be designed to detect a variety of characteristic informationfrom currency bills. Additionally these scanheads may employ a varietyof detection means such as magnetic or optical sensors. For example, avariety of currency characteristics can be measured using magneticsensing. These include detection of patterns of changes in magnetic flux(U.S. Pat. No. 3,280,974), patterns of vertical grid lines in theportrait area of bills (U.S. Pat. No. 3,870,629), the presence of asecurity thread (U.S. Pat. No. 5,151,607), total amount of magnetizablematerial of a bill (U.S. Pat. No. 4,617,458), patterns from sensing thestrength of magnetic fields along a bill (U.S. Pat. No. 4,593,184), andother patterns and counts from scanning different portions of the billsuch as the area in which the denomination is written out (U.S. Pat. No.4,356,473).

With regard to optical sensing, a variety of currency characteristicscan be measured such as density (U.S. Pat. No. 4,381,447), color (U.S.Pat. Nos. 4,490,846; 3,496,370; 3,480,785), length and thickness (U.S.Pat. No. 4,255,651), the presence of a security thread (U.S. Pat. No.5,151,607) and holes (U.S. Pat. No. 4,381,447), and other patterns ofreflectance and transmission (U.S. Pat. Nos. 3,496,370; 3,679,314;3,870,629; 4,179,685). Color detection techniques may employ colorfilters, colored lamps, and/or dichroic beamsplitters (U.S. Pat. Nos.4,841,358; 4,658,289; 4,716,456; 4,825,246, 4,992,860 and EP 325,364).Prescribed hues or intensities of a given color may be detected.Reflection and/or fluorescence of ultraviolet light may also be used, asdescribed in detail below. Absorption of infrared light may also be usedas an authenticating technique.

In addition to magnetic and optical sensing, other techniques ofdetecting characteristic information of currency include electricalconductivity sensing, capacitive sensing (U.S. Pat. Nos. 5,122,754watermark, security thread!; 3,764,899 thickness!; 3,815,021 dielectricproperties!; 5,151,607 security thread!), and mechanical sensing (U.S.Pat. Nos. 4,381,447 limpness!; 4,255,651 thickness!), and hologram,kinegram and moviegram sensing.

The detection of the borderline 17a realizes improved discriminationefficiency in systems designed to accommodate U.S. currency since theborderline 17a serves as an absolute reference point for initiation ofsampling. When the edge of a bill is used as a reference point, relativedisplacement of sampling points can occur because of the random mannerin which the distance from the edge to the borderline 17a varies frombill to bill due to the relatively large range of tolerances permittedduring printing and cutting of currency bills. As a result, it becomesdifficult to establish direct correspondence between sample points insuccessive bill scans and the discrimination efficiency is adverselyaffected. Accordingly, the modified pattern generation method discussedbelow is useful in discrimination systems designed to accommodate billsother than U.S. currency because many non-U.S. bills lack a borderlinearound the printed indicia on their bills. Likewise, the modifiedpattern generation method may be important in discrimination systemsdesigned to accommodate bills other than U.S. currency because theprinted indicia of many non-U.S. bills lack sharply defined edges whichin turns inhibits using the edge of the printed indicia of a bill as atrigger for the initiation of the scanning process and instead promotesreliance on using the edge of the bill itself as the trigger for theinitiation of the scanning process.

The use of the optical encoder 32 for controlling the sampling processrelative to the physical movement of a bill 17 across the scanheads 18a,18b is also advantageous in that the encoder 32 can be used to provide apredetermined delay following detection of the borderline 17a prior toinitiation of samples. The encoder delay can be adjusted in such a waythat the bill 17 is scanned only across those segments which contain themost distinguishable printed indicia relative to the different currencydenominations.

In the case of U.S. currency, for instance, it has been determined thatthe central, approximately two-inch (approximately 5 cm) portion ofcurrency bills, as scanned across the central section of the narrowdimension of the bill, provides sufficient data for distinguishing amongthe various U.S. currency denominations. Accordingly, the opticalencoder can be used to control the scanning process so that reflectancesamples are taken for a set period of time and only after a certainperiod of time has elapsed after the borderline 17a is detected, therebyrestricting the scanning to the desired central portion of the narrowdimension of the bill.

FIGS. 3-5b illustrate the scanning process in more detail. Referring toFIG. 4a, as a bill 17 is advanced in a direction parallel to the narrowedges of the bill, scanning via a slit in the scanhead 18a or 18b iseffected along a segment S of the central portion of the bill 17. Thissegment S begins a fixed distance D inboard of the borderline 17a. Asthe bill 17 traverses the scanhead, a strip s of the segment S is alwaysilluminated, and the photodetector 26 produces a continuous outputsignal which is proportional to the intensity of the light reflectedfrom the illuminated strip s at any given instant. This output issampled at intervals controlled by the encoder, so that the samplingintervals are precisely synchronized with the movement of the billacross the scanhead. FIG. 4b is similar to FIG. 4a but illustratesscanning along the wide dimension of the bill 17.

As illustrated in FIGS. 3, 5a, and 5b, it is preferred that the samplingintervals be selected so that the strips s that are illuminated forsuccessive samples overlap one another. The odd-numbered andeven-numbered sample strips have been separated in FIGS. 3, 5a, and 5bto more clearly illustrate this overlap. For example, the first andsecond strips s1 and s2 overlap each other, the second and third stripss2 and s3 overlap each other, and so on. Each adjacent pair of stripsoverlap each other. In the illustrative example, this is accomplished bysampling strips that are 0.050 inch (0.127 cm) wide at 0.029 inch (0.074cm) intervals, along a segment S that is 1.83 inch (4.65 cm) long (64samples).

FIGS. 6a and 6b illustrate two opposing surfaces of U.S. bills. Theprinted patterns on the black and green surfaces of the bill are eachenclosed by respective thin borderlines B₁ and B₂. As a bill is advancedin a direction parallel to the narrow edges of the bill, scanning viathe wide slit of one of the scanheads is effected along a segment S_(A)of the central portion of the black surface of the bill (FIG. 6a). Aspreviously stated, the orientation of the bill along the transport pathdetermines whether the upper or lower scanhead scans the black surfaceof the bill. This segment S_(A) begins a fixed distance D₁ inboard ofthe borderline B₁, which is located a distance W₁ from the edge of thebill. The scanning along segment S_(A) is as described in connectionwith FIGS. 3, 4a, and 5a.

Similarly, the other of the two scanheads scans a segment S_(B) of thecentral portion of the green surface of the bill (FIG. 6b). Theorientation of the bill along the transport path determines whether theupper or lower scanhead scans the green surface of the bill. Thissegment S_(B) begins a fixed distance D₂ inboard of the border line B₂,which is located a distance W₂ from the edge of the bill. For U.S.currency, the distance W₂ on the green surface is greater than thedistance W₁ on the black surface. It is this feature of U.S. currencywhich permits one to determine the orientation of the bill relative tothe upper and lower scanheads 18, thereby permitting one to select onlythe data samples corresponding to the green surface for correlation tothe master characteristic patterns in the EPROM 34. The scanning alongsegment S_(B) is as described in connection with FIGS. 3, 4a, and 5a.

FIGS. 6c and 6d are side elevations of FIG. 2a. FIG. 6c shows the firstsurface of a bill scanned by an upper scanhead and the second surface ofthe bill scanned by a lower scanhead, while FIG. 6d shows the firstsurface of a bill scanned by a lower scanhead and the second surface ofthe bill scanned by an upper scanhead. FIGS. 6c and 6d illustrate thepair of optical scanheads 18a, 18b disposed on opposite sides of thetransport path to permit optical scanning of both surfaces of a bill.With respect to United States currency, these opposing surfacescorrespond to the black and green surfaces of a bill. One of the opticalscanheads 18 (the "upper" scanhead 18a in FIGS. 6c-6d) is positionedabove the transport path and illuminates a light strip upon a firstsurface of the bill, while the other of the optical scanheads 18 (the"lower" scanhead 18b in FIGS. 6c-6d) is positioned below the transportpath and illuminates a light strip upon the second surface of the bill.The surface of the bill scanned by each scanhead 18 is determined by theorientation of the bill relative to the scanheads 18. The upper scanhead18a is located slightly upstream relative to the lower scanhead 18b.

The photodetector of the upper scanhead 18a produces a first analogoutput corresponding to the first surface of the bill, while thephotodetector of the lower scanhead 18b produces a second analog outputcorresponding to the second surface of the bill. The first and secondanalog outputs are converted into respective first and second digitaloutputs by means of respective analog-to-digital (ADC) convertor units28 whose outputs are fed as digital inputs to a central processing unit(CPU) 30. As described in detail below, the CPU 30 uses the sequence ofoperations illustrated in FIG. 12 to determine which of the first andsecond digital outputs corresponds to the green surface of the bill, andthen selects the "green" digital output for subsequent correlation to aseries of master characteristic patterns stored in EPROM 34. Asexplained below, the master characteristic patterns are preferablygenerated by performing scans on the green surfaces, not black surfaces,of bills of different denominations. According to a preferredembodiment, the analog output corresponding to the black surface of thebill is not used for subsequent correlation.

The optical sensing and correlation technique is based upon using theabove process to generate a series of stored intensity signal patternsusing genuine bills for each denomination of currency that is to bedetected. According to a preferred embodiment, two or four sets ofmaster intensity signal samples are generated and stored within thesystem memory, preferably in the form of an EPROM 34 (see FIG. 2a), foreach detectable currency denomination. According to one preferredembodiment these are sets of master green-surface intensity signalsamples. In the case of U.S. currency, the sets of master intensitysignal samples for each bill are generated from optical scans, performedon the green surface of the bill and taken along both the "forward" and"reverse" directions relative to the pattern printed on the bill.Alternatively, the optical scanning may be performed on the black sideof U.S. currency bills or on either surface of foreign bills.Additionally, the optical scanning may be performed on both sides of abill.

In adapting this technique to U.S. currency, for example, sets of storedintensity signal samples are generated and stored for seven differentdenominations of U.S. currency, i.e., $1, $2, $5, $10, $20, $50 and$100. For bills which produce significant pattern changes when shiftedslightly to the left or right, such as the $2, the $10 and/or the $100bills in U.S. currency, it is preferred to store two green-side patternsfor each of the "forward" and "reverse" directions, each pair ofpatterns for the same direction represent two scan areas that areslightly displaced from each other along the long dimension of the bill.Accordingly, a set of 16 or 18! different green-side mastercharacteristic patterns are stored within the EPROM for subsequentcorrelation purposes (four master patterns for the $10 bill or fourmaster patterns for the $10 bill and the $2 bill and/or the $100 bill!and two master patterns for each of the other denominations). Thegeneration of the master patterns is discussed in more detail below.Once the master patterns have been stored, the pattern generated byscanning a bill under test is compared by the CPU 30 with each of the 16or 18! master patterns of stored intensity signal samples to generate,for each comparison, a correlation number representing the extent ofcorrelation, i.e., similarity between corresponding ones of theplurality of data samples, for the sets of data being compared.

According to a preferred embodiment, in addition to the above set of 18original green-side master patterns, five more sets of green-side masterpatterns are stored in memory. These sets are explained more fully inconjunction with FIGS. 18a and 18b below.

The CPU 30 is programmed to identify the denomination of the scannedbill as corresponding to the set of stored intensity signal samples forwhich the correlation number resulting from pattern comparison is foundto be the highest. In order to preclude the possibility ofmischaracterizing the denomination of a scanned bill, as well as toreduce the possibility of spurious notes being identified as belongingto a valid denomination, a bi-level threshold of correlation is used asthe basis for making a "positive" call. If a "positive" call can not bemade for a scanned bill, an error signal is generated.

According to a preferred embodiment, master patterns are also stored forselected denominations corresponding to scans along the black side ofU.S. bills. More particularly, according to a preferred embodiment,multiple black-side master patterns are stored for $20, $50 and $100bills. For each of these denominations, three master patterns are storedfor scans in the forward and reverse directions for a total of sixpatterns for each denomination. For a given scan direction, black-sidemaster patterns are generated by scanning a corresponding denominatedbill along a segment located about the center of the narrow dimension ofthe bill, a segment slightly displaced (0.2 inches) to the left ofcenter, and a segment slightly displaced (0.2 inches) to the right ofcenter. When the scanned pattern generated from the green side of a testbill fails to sufficiently correlate with one of the green-side masterpatterns, the scanned pattern generated from the black side of a testbill is then compared to black-side master patterns in some situationsas described in more detail below in conjunction with FIGS. 19a-19c.

Using the above sensing and correlation approach, the CPU 30 isprogrammed to count the number of bills belonging to a particularcurrency denomination as part of a given set of bills that have beenscanned for a given scan batch, and to determine the aggregate total ofthe currency amount represented by the bills scanned during a scanbatch. The CPU 30 is also linked to an output unit 36 (FIGS. 2a and FIG.2b) which is adapted to provide a display of the number of billscounted, the breakdown of the bills in terms of currency denomination,and the aggregate total of the currency value represented by countedbills. The output unit 36 can also be adapted to provide a print-out ofthe displayed information in a desired format.

Referring again to the preferred embodiment depicted in FIG. 2d, as aresult of the first comparison described above based on the reflectedlight intensity information retrieved by scanhead 18, the CPU 30 willhave either determined the denomination of the scanned bill 17 ordetermined that the first scanned signal samples fail to sufficientlycorrelate with any of the sets of stored intensity signal samples inwhich case an error is generated. Provided that an error has not beengenerated as a result of this first comparison based on reflected lightintensity characteristics, a second comparison is performed. This secondcomparison is performed based on a second type of characteristicinformation, such as alternate reflected light properties, similarreflected light properties at alternate locations of a bill, lighttransmissivity properties, various magnetic properties of a bill, thepresence of a security thread embedded within a bill, the color of abill, the thickness or other dimension of a bill, etc. The second typeof characteristic information is retrieved from a scanned bill by thesecond scanhead 39. The scanning and processing by scanhead 39 may becontrolled in a manner similar to that described above with regard toscanhead 18.

In addition to the sets of stored first characteristic information, inthis example stored intensity signal samples, the EPROM 34 stores setsof stored second characteristic information for genuine bills of thedifferent denominations which the system 10 is capable of handling.Based on the denomination indicated by the first comparison, the CPU 30retrieves the set or sets of stored second characteristic data for agenuine bill of the denomination so indicated and compares the retrievedinformation with the scanned second characteristic information. Ifsufficient correlation exists between the retrieved information and thescanned information, the CPU 30 verifies the genuineness of the scannedbill 17. Otherwise, the CPU generates an error. While the preferredembodiment illustrated in FIG. 2d depicts a single CPU 30 for makingcomparisons of first and second characteristic information and a singleEPROM 34 for storing first and second characteristic information, it isunderstood that two or more CPUs and/or EPROMs could be used, includingone CPU for making first characteristic information comparisons and asecond CPU for making second characteristic information comparisons.Using the above sensing and correlation approach, the CPU 30 isprogrammed to count the number of bills belonging to a particularcurrency denomination whose genuineness has been verified as part of agiven set of bills that have been scanned for a given scan batch, and todetermine the aggregate total of the currency amount represented by thebills scanned during a scan batch.

Referring now to FIGS. 7a and 7b, there is shown a representation, inblock diagram form, of a preferred circuit arrangement for processingand correlating reflectance data according to the system of thisinvention. The CPU 30 accepts and processes a variety of input signalsincluding those from the optical encoder 32, the sensor 26 and theerasable programmable read only memory (EPROM) 60. The EPROM 60 hasstored within it the correlation program on the basis of which patternsare generated and test patterns compared with stored master programs inorder to identify the denomination of test currency. A crystal 40 servesas the time base for the CPU 30, which is also provided with an externalreference voltage V_(REF) 42 on the basis of which peak detection ofsensed reflectance data is performed.

According to one embodiment, the CPU 30 also accepts a timer resetsignal from a reset unit 44 which, as shown in FIG. 7b, accepts theoutput voltage from the photodetector 26 and compares it, by means of athreshold detector 44a, relative to a pre-set voltage threshold,typically 5.0 volts, to provide a reset signal which goes "high" when areflectance value corresponding to the presence of paper is sensed. Morespecifically, reflectance sampling is based on the premise that noportion of the illuminated light strip (24 in FIG. 2a) is reflected tothe photodetector in the absence of a bill positioned below thescanhead. Under these conditions, the output of the photodetectorrepresents a "dark" or "zero" level reading. The photodetector outputchanges to a "white" reading, typically set to have a value of about 5.0volts, when the edge of a bill first becomes positioned below thescanhead and falls under the light strip 24. When this occurs, the resetunit 44 provides a "high" signal to the CPU 30 and marks the initiationof the scanning procedure.

The machine-direction dimension, that is, the dimension parallel to thedirection of bill movement, of the illuminated strip of light producedby the light sources within the scanhead is set to be relatively smallfor the initial stage of the scan when the thin borderline is beingdetected, according to a preferred embodiment. The use of the narrowslit increases the sensitivity with which the reflected light isdetected and allows minute variations in the "gray" level reflected offthe bill surface to be sensed. This ensures that the thin borderline ofthe pattern, i.e., the starting point of the printed pattern on thebill, is accurately detected. Once the borderline has been detected,subsequent reflectance sampling is performed on the basis of arelatively wider light strip in order to completely scan across thenarrow dimension of the bill and obtain the desired number of samples,at a rapid rate. The use of a wider slit for the actual sampling alsosmoothes out the output characteristics of the photodetector andrealizes the relatively large magnitude of analog voltage which isdesirable for accurate representation and processing of the detectedreflectance values.

The CPU 30 processes the output of the sensor 26 through a peak detector50 which essentially functions to sample the sensor output voltage andhold the highest, i.e., peak, voltage value encountered after thedetector has been enabled. For U.S. currency, the peak detector is alsoadapted to define a scaled voltage on the basis of which the printedborderline on the currency bills is detected. The output of the peakdetector 50 is fed to a voltage divider 54 which lowers the peak voltagedown to a scaled voltage V_(S) representing a predefined percentage ofthis peak value. The voltage V_(S) is based upon the percentage drop inoutput voltage of the peak detector as it reflects the transition fromthe "high" reflectance value resulting from the scanning of theunprinted edge portions of a currency bill to the relatively lower"gray" reflectance value resulting when the thin borderline isencountered. Preferably, the scaled voltage V_(S) is set to be about70-80 percent of the peak voltage.

The scaled voltage V_(S) is supplied to a line detector 56 which is alsoprovided with the incoming instantaneous output of the sensor 26. Theline detector 56 compares the two voltages at its input side andgenerates a signal L_(DET) which normally stays "low" and goes "high"when the edge of the bill is scanned. The signal L_(DET) goes "low" whenthe incoming sensor output reaches the pre-defined percentage of thepeak output up to that point, as represented by the voltage V_(S). Thus,when the signal L_(DET) goes "low", it is an indication that theborderline of the bill pattern has been detected. At this point, the CPU30 initiates the actual reflectance sampling under control of theencoder 32, and the desired fixed number of reflectance samples areobtained as the currency bill moves across the illuminated light stripand is scanned along the central section of its narrow dimension.

When master characteristic patterns are being generated, the reflectancesamples resulting from the scanning of one or more genuine bills foreach denomination are loaded into corresponding designated sectionswithin a system memory 60, which is preferably an EPROM. During currencydiscrimination, the reflectance values resulting from the scanning of atest bill are sequentially compared, under control of the correlationprogram stored within the EPROM 60, with the corresponding mastercharacteristic patterns stored within the EPROM 60. A pattern averagingprocedure for scanning bills and generating characteristic patterns isdescribed below in connection with FIGS. 15a-15e.

The interrelation between the use of the first and second type ofcharacteristic information can be seen by considering FIGS. 8a and 8bwhich comprise a flowchart illustrating the sequence of operationsinvolved in implementing a discrimination and authentication systemaccording to a preferred embodiment of the present invention. Upon theinitiation of the sequence of operations (step 1748), reflected lightintensity information is retrieved from a bill being scanned (step1750). Similarly, second characteristic information is also retrievedfrom the bill being scanned (step 1752). Denomination error and secondcharacteristic error flags are cleared (steps 1753 and 1754).

Next the scanned intensity information is compared to each set of storedintensity information corresponding to genuine bills of alldenominations the system is programmed to accommodate (step 1758). Foreach denomination, a correlation number is calculated. The system then,based on the correlation numbers calculated, determines either thedenomination of the scanned bill or generates a denomination error bysetting the denomination error flag steps 1760 and 1762). In the casewhere the denomination error flag is set (step 1762), the process isended (step 1772). Alternatively, if based on this first comparison, thesystem is able to determine the denomination of the scanned bill, thesystem proceeds to compare the scanned second characteristic informationwith the stored second characteristic information corresponding to thedenomination determined by the first comparison (step 1764).

For example, if as a result of the first comparison the scanned bill isdetermined to be a $20 bill, the scanned second characteristicinformation is compared to the stored second characteristic informationcorresponding to a genuine $20 bill. In this manner, the system need notmake comparisons with stored second characteristic information for theother denominations the system is programmed to accommodate. If based onthis second comparison (step 1764) it is determined that the scannedsecond characteristic information does not sufficiently match that ofthe stored second characteristic information (step 1766), then a secondcharacteristic error is generated by setting the second characteristicerror flag (step 1768) and the process is ended (step 1772). If thesecond comparison results in a sufficient match between the scanned andstored second characteristic information (step 1766), then thedenomination of the scanned bill is indicated (step 1770) and theprocess is ended (step 1772).

An example of an interrelationship between authentication based on firstand second characteristics can be seen by considering Table 1. Thedenomination determined by optical scanning of a bill is preferably usedto facilitate authentication of the bill by magnetic scanning, using therelationship set forth in Table 1.

                  TABLE 1    ______________________________________             Sensitivity    Denomination               1        2      3      4    5    ______________________________________     $1        200      250    300    375  450     $2        100      125    150    225  300     $5        200      250    300    350  400    $10        100      125    150    200  250    $20        120      150    180    270  360    $50        200      250    300    375  450    $100       100      125    150    250  350    ______________________________________

Table 1 depicts relative total magnetic content thresholds for variousdenominations of genuine bills. Columns 1.5 represent varying degrees ofsensitivity. The values in Table 1 are set based on the scanning ofgenuine bills of varying denominations for total magnetic content andsetting required thresholds based on the degree of sensitivity selected.The information in Table 1 is based on the total magnetic content of agenuine $1 being 1000. The following discussion is based on asensitivity setting of 4. In this example it is assumed that magneticcontent represents the second characteristic tested. If the comparisonof first characteristic information, such as reflected light intensity,from a scanned billed and stored information corresponding to genuinebills results in an indication that the scanned bill is a $10denomination, then the total magnetic content of the scanned bill iscompared to the total magnetic content threshold of a genuine $10 bill,i.e., 200. If the magnetic content of the scanned bill is less than 200,the bill is rejected. Otherwise it is accepted as a $10 bill.

Referring now to FIGS. 9-11b, there are shown flow charts illustratingthe sequence of operations involved in implementing the above-describedoptical sensing and correlation technique. FIGS. 9 and 10, inparticular, illustrate the sequences involved in detecting the presenceof a bill adjacent the scanheads and the borderlines on each side of thebill. Turning to FIG. 9, at step 70, the lower scanhead fine lineinterrupt is initiated upon the detection of the fine line by the lowerscanhead. An encoder counter is maintained that is incremented for eachencoder pulse. The encoder counter scrolls from 0-65,535 and then startsat 0 again. At step 71 the value of the encoder counter is stored inmemory upon the detection of the fine line by the lower scanhead. Atstep 72 the lower scanhead fine line interrupt is disabled so that itwill not be triggered again during the interrupt period. At step 73, itis determined whether the magnetic sampling has been completed for theprevious bill. If it has not, the magnetic total for the previous billis stored in memory at step 74, and the magnetic sampling done flag isset at step 75 so that magnetic sampling of the present bill maythereafter be performed. Steps 74 and 75 are skipped if it is determinedat step 73 that the magnetic sampling has been completed for theprevious bill. At step 76, a lower scanhead bit in the trigger flag isset. This bit is used to indicate that the lower scanhead has detectedthe fine line. The magnetic sampler is initialized at step 77, and themagnetic sampling interrupt is enabled at step 78. A density sampler isinitialized at step 79, and a density sampling interrupt is enabled atstep 80. The lower read data sampler is initialized at step 81, and alower scanhead data sampling interrupt is enabled at step 82. At step83, the lower scanhead fine line interrupt flag is reset, and at step 84the program returns from the interrupt.

Turning to FIG. 10, at step 85, the upper scanhead fine line interruptis initiated upon the detection of the fine line by the upper scanhead.At step 86 the value of the encoder counter is stored in memory upon thedetection of the fine line by the upper scanhead. This information inconnection with the encoder counter value associated with the detectionof the fine line by the lower scanhead may then be used to determine theface orientation of a bill, that is whether a bill is fed green side upor green side down in the case of U.S. bills, as is described in moredetail below in connection with FIG. 12. At step 87 the upper scanheadfine line interrupt is disabled so that it will not be triggered againduring the interrupt period. At step 88, the upper scanhead bit in thetrigger flag is set. This bit is used to indicate that the upperscanhead has detected the fine line. By checking the lower and upperscanhead bits in the trigger flag, it can be determined whether eachside has detected a respective fine line. Next, the upper scanhead datasampler is initialized at step 89, and the upper scanhead data samplinginterrupt is enabled at step 90. At step 91, the upper scanhead fineline interrupt flag is reset, and at step 92 the program returns fromthe interrupt.

Referring now to FIGS. 11a and 11b, there are shown, respectively, thedigitizing routines associated with the lower and upper scanheads. FIG.11a is a flow chart illustrating the sequential procedure involved inthe analog-to-digital conversion routine associated with the lowerscanhead. The routine is started at step 93a. Next, the sample pointeris decremented at step 94a so as to maintain an indication of the numberof samples remaining to be obtained. The sample pointer provides anindication of the sample being obtained and digitized at a given time.At step 95a, the digital data corresponding to the output of thephotodetector associated with the lower scanhead for the current sampleis read. The data is converted to its final form at step 96a and storedwithin a pre-defined memory segment as X_(IN-L) at step 97a.

Next, at step 98a, a check is made to see if the desired fixed number ofsamples "N" has been taken. If the answer is found to be negative, step99a is accessed where the interrupt authorizing the digitization of thesucceeding sample is enabled, and the program returns from interrupt atstep 100a for completing the rest of the digitizing process. However, ifthe answer at step 98a is found to be positive, i.e., the desired numberof samples have already been obtained, a flag, namely the lower scanheaddone flag bit, indicating the same is set at step 101a, and the programreturns from interrupt at step 102a.

FIG. 11b is a flow chart illustrating the sequential procedure involvedin the analog-to-digital conversion routine associated with the upperscanhead. The routine is started at step 93b. Next, the sample pointeris decremented at step 94b so as to maintain an indication of the numberof samples remaining to be obtained. The sample pointer provides anindication of the sample being obtained and digitized at a given time.At step 95b, the digital data corresponding to the output of thephotodetector associated with the upper scanhead for the current sampleis read. The data is converted to its final form at step 96b and storedwithin a pre-defined memory segment as X_(IN-U) at step 97b.

Next, at step 98b, a check is made to see if the desired fixed number ofsamples "N" has been taken. If the answer is found to be negative, step99b is accessed where the interrupt authorizing the digitization of thesucceeding sample is enabled and the program returns from interrupt atstep 100b for completing the rest of the digitizing process. However, ifthe answer at step 98b is found to be positive, i.e., the desired numberof samples have already been obtained, a flag, namely the upper scanheaddone flag bit, indicating the same is set at step 101b, and the programreturns from interrupt at step 102b.

The CPU 30 is programmed with the sequence of operations in FIG. 12 tocorrelate at least initially only the test pattern corresponding to thegreen surface of a scanned bill. As shown in FIGS. 6c-6d, the upperscanhead 18a is located slightly upstream adjacent the bill transportpath relative to the lower scanhead 18b. The distance between thescanheads 18a, 18b in a direction parallel to the transport pathcorresponds to a predetermined number of encoder counts. It should beunderstood that the encoder 32 produces a repetitive tracking signalsynchronized with incremental movements of the bill transport mechanism,and this repetitive tracking signal has a repetitive sequence of counts(e.g., 65,535 counts) associated therewith. As a bill is scanned by theupper and lower scanheads 18a, 18b, the CPU 30 monitors the output ofthe upper scanhead 18a to detect the borderline of a first bill surfacefacing the upper scanhead 18a. Once this borderline of the first surfaceis detected, the CPU 30 retrieves and stores a first encoder count inmemory. Similarly, the CPU 30 monitors the output of the lower scanhead18b to detect the borderline of a second bill surface facing the lowerscanhead 18b. Once the borderline of the second surface is detected, theCPU 30 retrieves and stores a second encoder count in memory.

Referring to FIG. 12, the CPU 30 is programmed to calculate thedifference between the first and second encoder counts (step 105a). Ifthis difference is greater than the predetermined number of encodercounts corresponding to the distance between the scanheads 18a, 18b plussome safety factor number "X", e.g., 20 (step 106), the bill is orientedwith its black surface facing the upper scanhead 18a and its greensurface facing the lower scanhead 18b. This can best be understood byreference to FIG. 6c which shows a bill with the foregoing orientation.In this situation, once the borderline B₁ of the black surface passesbeneath the upper scanhead 18a and the first encoder count is stored,the borderline B₂ still must travel for a distance greater than thedistance between the upper and lower scanheads 18a, 18b in order to passover the lower scanhead 18b. As a result, the difference between thesecond encoder count associated with the borderline B₂ and the firstencoder count associated with the borderline B₁ will be greater than thepredetermined number of encoder counts corresponding to the distancebetween the scanheads 18a, 18b. With the bill oriented with its greensurface facing the lower scanhead, the CPU 30 sets a flag to indicatethat the test pattern produced by the lower scanhead 18b should becorrelated (step 107). Next, this test pattern is correlated with thegreen-side master characteristic patterns stored in memory (step 109).

If at step 106 the difference between the first and second encodercounts is less than the predetermined number of encoder countscorresponding to the distance between the scanheads 18a, 18b, the CPU 30is programmed to determine whether the difference between the first andsecond encoder counts is less than the predetermined number minus somesafety number "X", e.g., 20 (step 108). If the answer is negative, theorientation of the bill relative to the scanheads 18a, 18b is uncertain,so the CPU 30 is programmed to correlate the test patterns produced byboth the upper and lower scanheads 18a, 18b with the green-side mastercharacteristic patterns stored in memory (steps 109, 110, and 111).

If the answer is affirmative, the bill is oriented with its greensurface facing the upper scanhead 18a and its black surface facing thelower scanhead 18b. This can best be understood by reference to FIG. 6d,which shows a bill with the foregoing orientation. In this situation,once the borderline B₂ of the green surface passes beneath the upperscanhead 18a and the first encoder count is stored, the borderline B₁must travel for a distance less than the distance between the upper andlower scanheads 18a, 18b in order to pass over the lower scanhead 18b.As a result, the difference between the second encoder count associatedwith the borderline B₁ and the first encoder count associated with theborderline B₂ should be less than the predetermined number of encodercounts corresponding to the distance between the scanheads 18a, 18b. Tobe on the safe side, it is required that the difference between firstand second encoder counts be less than the predetermined number minusthe safety number "X". Therefore, the CPU 30 is programmed to correlatethe test pattern produced by the upper scanhead 18a with the green-sidemaster characteristic patterns stored in memory (step 111).

After correlating the test pattern associated with either the upperscanhead 18a, the lower scanhead 18b, or both scanheads 18a, 18b, theCPU 30 is programmed to perform the bi-level threshold check (step 112).

A simple correlation procedure is utilized for processing digitizedreflectance values into a form which is conveniently and accuratelycompared to corresponding values pre-stored in an identical format. Morespecifically, as a first step, the mean value X for the set of digitizedreflectance samples (comparing "n" samples) obtained for a bill scan runis first obtained as below: ##EQU1##

Subsequently, a normalizing factor Sigma ("σ") is determined as beingequivalent to the sum of the square of the difference between eachsample and the mean, as normalized by the total number n of samples.More specifically, the normalizing factor is calculated as below:##EQU2##

In the final step, each reflectance sample is normalized by obtainingthe difference between the sample and the above-calculated mean valueand dividing it by the square root of the normalizing factor σ asdefined by the following equation: ##EQU3##

The result of using the above correlation equations is that, subsequentto the normalizing process, a relationship of correlation exists betweena test pattern and a master pattern such that the aggregate sum of theproducts of corresponding samples in a test pattern and any masterpattern, when divided by the total number of samples, equals unity ifthe patterns are identical. Otherwise, a value less than unity isobtained. Accordingly, the correlation number or factor resulting fromthe comparison of normalized samples within a test pattern to those of astored master pattern provides a clear indication of the degree ofsimilarity or correlation between the two patterns.

According to a preferred embodiment of this invention, the fixed numberof reflectance samples which are digitized and normalized for a billscan is selected to be 64. It has experimentally been found that the useof higher binary orders of samples (such as 128, 256, etc.) does notprovide a correspondingly increased discrimination efficiency relativeto the increased processing time involved in implementing theabove-described correlation procedure. It has also been found that theuse of a binary order of samples lower than 64, such as 32, produces asubstantial drop in discrimination efficiency.

The correlation factor can be represented conveniently in binary termsfor ease of correlation. In a preferred embodiment, for instance, thefactor of unity which results when a hundred percent correlation existsis represented in terms of the binary number 2¹⁰, which is equal to adecimal value of 1024. Using the above procedure, the normalized sampleswithin a test pattern are compared to the master characteristic patternsstored within the system memory in order to determine the particularstored pattern to which the test pattern corresponds most closely byidentifying the comparison which yields a correlation number closest to1024.

A bi-level threshold of correlation is required to be satisfied before aparticular call is made, for at least certain denominations of bills.More specifically, the correlation procedure is adapted to identify thetwo highest correlation numbers resulting from the comparison of thetest pattern to one of the stored patterns. At that point, a minimumthreshold of correlation is required to be satisfied by these twocorrelation numbers. It has experimentally been found that a correlationnumber of about 850 serves as a good cut-off threshold above whichpositive calls may be made with a high degree of confidence and belowwhich the designation of a test pattern as corresponding to any of thestored patterns is uncertain. As a second threshold level, a minimumseparation is prescribed between the two highest correlation numbersbefore making a call. This ensures that a positive call is made onlywhen a test pattern does not correspond, within a given range ofcorrelation, to more than one stored master pattern. Preferably, theminimum separation between correlation numbers is set to be 150 when thehighest correlation number is between 800 and 850. When the highestcorrelation number is below 800, no call is made.

The procedure involved in comparing test patterns to master patterns isdiscussed below in connection with FIG. 18a.

Next a routine designated as "CORRES" is initiated. The procedureinvolved in executing the routine CORRES is illustrated at FIG. 13 whichshows the routine as starting at step 114. Step 115 determines whetherthe bill has been identified as a $2 bill, and, if the answer isnegative, step 116 determines whether the best correlation number ("call#1") is greater than 799. If the answer is negative, the correlationnumber is too low to identify the denomination of the bill withcertainty, and thus step 117 generates a "no call" code. A "no callprevious bill" flag is then set at step 118, and the routine returns tothe main program at step 119.

An affirmative answer at step 116 advances the system to step 120, whichdetermines whether the sample data passes an ink stain test (describedbelow). If the answer is negative, a "no call" code is generated at step117. If the answer is affirmative, the system advances to step 121 whichdetermines whether the best correlation number is greater than 849. Anaffirmative answer at step 121 indicates that the correlation number issufficiently high that the denomination of the scanned bill can beidentified with certainty without any further checking. Consequently, a"denomination" code identifying the denomination represented by thestored pattern resulting in the highest correlation number is generatedat step 122, and the system returns to the main program at step 119.

A negative answer at step 121 indicates that the correlation number isbetween 800 and 850. It has been found that correlation numbers withinthis range are sufficient to identify all bills except the $2 bill.Accordingly, a negative response at step 121 advances the system to step123 which determines whether the difference between the two highestcorrelation numbers ("call #1" and "call #2") is greater than 149. Ifthe answer is affirmative, the denomination identified by the highestcorrelation number is acceptable, and thus the "denomination" code isgenerated at step 122. If the difference between the two highestcorrelation numbers is less than 150, step 123 produces a negativeresponse which advances the system to step 117 to generate a "no call"code.

Returning to step 115, an affirmative response at this step indicatesthat the initial call is a $2 bill. This affirmative response initiatesa series of steps 124-127 which are identical to steps 116, 120, 121 and123 described above, except that the numbers 799 and 849 used in steps116 and 121 are changed to 849 and 899, respectively, in steps 124 and126. The result is either the generation of a "no call" code at step 117or the generation of a $2 "denomination" code at step 122.

One problem encountered in currency recognition and counting systems isthe difficulty involved in interrupting (for a variety of reasons) andresuming the scanning and counting procedure as a stack of bills isbeing scanned. If a particular currency recognition unit (CRU) has to behalted in operation due to a "major" system error, such as a bill beingjammed along the transport path, there is generally no concern about theoutstanding transitional status of the overall recognition and countingprocess. However, where the CRU has to be halted due to a "minor" error,such as the identification of a scanned bill as being a counterfeit(based on a variety of monitored parameters) or a "no call" (a billwhich is not identifiable as belonging to a specific currencydenomination based on the plurality of stored master patterns and/orother criteria), it is desirable that the transitional status of theoverall recognition and counting process be retained so that the CRU maybe restarted without any effective disruptions of therecognition/counting process.

More specifically, once a scanned bill has been identified as a "nocall" bill (B₁) based on some set of predefined criteria, it isdesirable that this bill B₁ be transported directly to a return conveyoror to the system stacker, and the CRU brought to a halt, while at thesame time ensuring that the following bills are maintained in positionsalong the bill transport path whereby CRU operation can be convenientlyresumed without any disruption of the recognition/counting process.

Since the bill processing speeds at which currency recognition systemsmust operate are substantially high (speeds of the order of 350 to 1500bills per minute), it is practically impossible to totally halt thesystem following a "no call" without the following bill B₂ alreadyoverlapping the optical scanhead and being partially scanned. As aresult, it is virtually impossible for the CRU system to retain thetransitional status of the recognition/counting process (particularlywith respect to bill B₂) in order that the process may be resumed oncethe bad bill B₁ has been dealt with, and the system restarted. The basicproblem is that if the CRU is halted with bill B₂ only partiallyscanned, it is difficult to reference the data reflectance samplesextracted therefrom in such a way that the scanning may be latercontinued (when the CRU is restarted) from exactly the same point wherethe sample extraction process was interrupted when the CRU was stopped.

Even if an attempt were made at immediately halting the CRU systemfollowing a "no call," any subsequent scanning of bills would be totallyunreliable because of mechanical backlash effects and the resultantdisruption of the optical encoder routine used for bill scanning.Consequently, when the CRU is restarted, the call for the following billis also likely to be bad and the overall recognition/counting process istotally disrupted as a result of an endless loop of "no calls."

The above problems are solved by the use of a currency detecting andcounting technique whereby a scanned bill identified as a "no call" istransported directly to the return conveyor which returns the bill tothe customer, while the CRU is halted without adversely affecting thedata collection and processing steps for a succeeding bill. Accordingly,when the CRU is restarted, the overall bill recognition and countingprocedure can be resumed without any disruption as if the CRU had neverbeen halted at all.

According to a preferred technique, if the bill is identified as a "nocall" based on any of a variety of conventionally defined bill criteria,the CRU is subjected to a controlled deceleration process whereby thespeed at which bills are moved across the scanhead is reduced from thenormal operating speed. During this deceleration process the "no call"bill (B₁) is transported to the return conveyor, at the same time, thefollowing bill B₂ is subjected to the standard scanning procedure inorder to identify the denomination.

The rate of deceleration is such that optical scanning of bill B₂ iscompleted by the time the CRU operating speed is reduced to a predefinedoperating speed. While the exact operating speed at the end of thescanning of bill B₂ is not critical, the objective is to permit completescanning of bill B₂ without subjecting it to backlash effects that wouldresult if the ramping were too fast, while at the same time ensuringthat bill B₁ has in fact been transported to the return conveyor.

It has been experimentally determined that at nominal operating speedsof the order of 1000 bills per minute, the deceleration is preferablysuch that the CRU operating speed is reduced to about one-fifth of itsnormal operating speed at the end of the deceleration phase, i.e., bythe time optical scanning of bill B₂ has been completed. It has beendetermined that at these speed levels, positive calls can be made as tothe denomination of bill B₂ based on reflectance samples gathered duringthe deceleration phase with a relatively high degree of certainty (i.e.,with a correlation number exceeding about 850).

Once the optical scanning of bill B₂ has been completed, the speed isreduced to an even slower speed until the bill B₂ has passed bill-edgesensors S1 and S2 described below, and the bill B₂ is then brought to acomplete stop. At the same time, the results of the processing ofscanned data corresponding to bill B₂ are stored in system memory. Theultimate result of this stopping procedure is that the CRU is brought toa complete halt following the point where the scanning of bill B₂ hasbeen reliably completed, and the scan procedure is not subjected to thedisruptive effects (backlash, etc.) which would result if a completehalt were attempted immediately after bill B₁ is identified as a "nocall."

The reduced operating speed of the machine at the end of thedeceleration phase is such that the CRU can be brought to a total haltbefore the next following bill B₃ has been transported over the opticalscanhead. Thus, when the CRU is in fact halted, bill B₁ is in the returnconveyor, bill B₂ is maintained in transit between the optical scanheadand the stacking station after it has been subjected to scanning, andthe following bill B₃ is stopped short of the optical scanhead.

When the CRU is restarted, the overall scanning operation can be resumedin an uninterrupted fashion by using the stored call results for bill B₂as the basis for updating the system count appropriately, moving bill B₂from its earlier transitional position along the transport path into thestacking station, and moving bill B₃ along the transport path into theoptical scanhead area where it can be subjected to normal scanning andprocessing. A routine for executing the deceleration/stopping proceduredescribed above is illustrated by the flow chart in FIG. 14. Thisroutine is initiated at step 170 with the CRU in its normal operatingmode. At step 171, a test bill B₁ is scanned and the data reflectancesamples resulting therefrom are processed. Next, at step 172, adetermination is made as to whether or not test bill B₁ is a "no call"using predefined criteria in combination with the overall billrecognition procedure, such as the routine of FIG. 13. If the answer atstep 172 is negative, i.e., the test bill B₁ can be identified, step 173is accessed where normal bill processing is continued in accordance withthe procedures described above. If, however, the test bill B₁ is foundto be a "no call" at step 172, step 174 is accessed where CRUdeceleration is initiated, e.g., the transport drive motor speed isreduced to about one-fifth its normal speed.

Subsequently, the "no call" bill B₁ is guided to the return conveyorwhile, at the same time, the following test bill B₂ is brought under theoptical scanhead and subjected to the scanning and processing steps. Thecall resulting from the scanning and processing of bill B₂ is stored insystem memory at this point. Step 175 determines whether the scanning ofbill B₂ is complete. When the answer is negative, step 176 determineswhether a preselected "bill timeout" period has expired so that thesystem does not wait for the scanning of a bill that is not present. Anaffirmative answer at step 176 results in the transport drive motorbeing stopped at step 179 while a negative answer at step 176 causessteps 175 and 176 to be reiterated until one of them produces anaffirmative response.

After the scanning of bill B₂ is complete and before stopping thetransport drive motor, step 178 determines whether either of the sensorsS1 or S2 (described below) is covered by a bill. A negative answer atstep 178 indicates that the bill has cleared both sensors S1 and S2, andthus the transport drive motor is stopped at step 179. This signifiesthe end of the deceleration/stopping process. At this point in time,bill B₂ remains in transit while the following bill B₃ is stopped on thetransport path just short of the optical scanhead.

Following step 179, corrective action responsive to the identificationof a "no call" bill is conveniently undertaken, and the CRU is then incondition for resuming the scanning process. Accordingly, the CRU can berestarted and the stored results corresponding to bill B₂, are used toappropriately update the system count. Next, the identified bill B₂ isguided along the transport path to the stacking station, and the CRUcontinues with its normal processing routine. While the abovedeceleration process has been described in the context of a "no call"error, other minor errors (e.g., suspect bills, stranger bills instranger mode, etc.) are handled in the same manner.

In currency discrimination systems in which discrimination is based onthe comparison of a pattern obtained from scanning a subject bill tostored master patterns corresponding to various denominations, thepatterns which are designated as master patterns significantly influencethe performance characteristics of the discrimination system. Accordingto a preferred technique, a master pattern for a given denomination isgenerated by averaging a plurality of component patterns. Each componentpattern is generated by scanning a genuine bill of the givendenomination.

According to a first method, master patterns are generated by scanning astandard bill a plurality of times, typically three (3) times, andobtaining the average of corresponding data samples before storing theaverage as representing a master pattern. In other words, a masterpattern for a given denomination is generated by averaging a pluralityof component patterns, wherein all of the component patterns aregenerated by scanning a single genuine bill of "standard" quality of thegiven denomination. The "standard" bill is a slightly used bill, asopposed to a crisp new bill or one which has been subject to a highdegree of usage. Rather, the standard bill is a bill of good to averagequality. Component patterns generated according to this first methodsare illustrated in FIGS. 15a-15c. More specifically, FIGS. 15a-15c showthree test patterns generated, respectively, for the forward scanning ofa $1 bill along its green side, the reverse scanning of a $2 bill on itsgreen side, and the forward scanning of a $100 bill on its green side.It should be noted that, for purposes of clarity the test patterns inFIGS. 15a-15c were generated by using 128 reflectance samples per billscan, as opposed to the preferred use of only 64 samples. The markeddifference existing among corresponding samples for these three testpatterns is indicative of the high degree of confidence with whichcurrency denominations may be called using the foregoing optical sensingand correlation procedure.

According to a second method, a master pattern for a given denominationis generated by scanning two or more standard bills of standard qualityand obtaining a plurality of component patterns. These componentpatterns are then averaged in deriving a master pattern. For example, ithas been found that some genuine $5 bills have dark stairs on theLincoln Memorial while other genuine $5 bills have light stairs. Tocompensate for this variation, standard bills for which componentpatterns are derived may be chosen with at least one standard billscanned having dark stairs and with at least one standard bill havinglight stairs.

It has been found that an alternate method can lead to improvedperformance in a discrimination systems, especially with regards tocertain denominations. For example, it has been found that the printedindicia on a $10 bill has changed slightly with 1990 series billsincorporating security threads. More specifically, 1990 series $10 billshave a borderline-to-borderline dimension which is slightly greater thanprevious series $10 bills. Likewise it has been found that the scannedpattern of an old, semi-shrunken $5 bill can differ significantly fromthe scanned pattern of a new $5 bill.

According to a third method, a master pattern for a given denominationis generated by averaging a plurality of component patterns, whereinsome of the component patterns are generated by scanning one or more newbills of the given denomination, and some of the component patterns aregenerated by scanning one or more old bills of the given denomination.New bills are bills of good quality which have been printed in recentyears and have a security thread incorporated therein (for thosedenominations in which security threads are placed). New bills arepreferably relatively crisp. A new $10 bill is preferably a 1990 seriesor later bill of very high quality, meaning that the bill is in nearmint condition. Old bills are bills exhibiting some shrinkage and oftensome discoloration. Shrinkage may result from a bill having beensubjected to a relatively high degree of use. A new bill utilized inthis third method is of higher quality than a standard bill of theprevious methods, while an old bill in this third method is of lowerquality than a standard bill.

The third method can be understood by considering Table 2 whichsummarizes the manner in which component patterns are generated for avariety of denominations.

                  TABLE 2    ______________________________________    Component Scans by Denomination    Denomination             Scan Direction                         CP1      CP2     CP3    ______________________________________     $1      Forward     -0.2 std .sup. 0.0 std                                          +0.2 std     $1      Reverse     -0.2 std .sup. 0.0 std                                          +0.2 std     $2, left             Forward     -0.2 std -0.15 std                                          -0.1 std     $2, left             Reverse     -0.2 std -0.15 std                                          -0.1 std     $2, right             Forward     .sup. 0.0 std                                  +0.1 std                                          +0.2 std     $2, right             Reverse     .sup. 0.0 std                                  +0.1 std                                          +0.2 std     $5      Forward     -0.2 old .sup. 0.0 new                                          +0.2 old                         (lt str) (dk str)                                          (lt str)     $5      Reverse     -0.2 old .sup. 0.0 new                                          +0.2 old                         (lt str) (dk str)                                          (lt str)     $10, left             Forward     -0.2 old -0.1 new                                          .sup. 0.0 old     $10, left             Reverse     .sup. 0.0 old                                  +0.1 new                                          +0.2 old     $10, right             Forward     +0.1 old +0.2 new                                          +0.3 old     $10, right             Reverse     -0.2 old -0.15 new                                          -0.1 old     $20     Forward     -0.2 old .sup. 0.0 new                                          +0.2 old     $20     Reverse     -0.2 old .sup. 0.0 new                                          +0.2 old     $50     Forward     -0.2 std .sup. 0.0 std                                          +0.2 std     $50     Reverse     -0.2 std .sup. 0.0 std                                          +0.2 std    $100     Forward     -0.2 std .sup. 0.0 std                                          +0.2 std    $100     Reverse     -0.2 std .sup. 0.0 std                                          +0.2 std    ______________________________________

Table 2 summarizes the position of the scanhead relative to the centerof the green surface of United States currency as well as the type ofbill to be scanned for generating component patterns for variousdenominations. The three component patterns ("CP") for a givendenomination and for a given scan direction are averaged to yield acorresponding master pattern. The eighteen (18) rows correspond to thepreferred method of storing eighteen (18) master patterns. The scanheadposition is indicated relative to the center of the borderlined area ofthe bill. Thus a position of "0.0" indicates that the scanhead iscentered over the center of the borderlined area of the bill.Displacements to the left of center are indicated by negative numbers,while displacements to the right are indicated by positive numbers. Thusa position of "-0.2" indicates a displacement of 2/10th of an inch tothe left of the center of a bill, while a position of "+0.1" indicates adisplacement of 1/10ths of an inch to the right of the center of a bill.

Accordingly, Table 2 indicates that component patterns for a $20 billscanned in the forward direction are obtained by scanning an old $20bill 2/10ths of a inch to the right and to the left of the center of thebill and by scanning a new $20 bill directly down the center of thebill. FIG. 15d is a graph illustrating these three patterns. These threepatterns are then averaged to obtain the master pattern for a $20 billscanned in the forward direction. FIG. 15e is a graph illustrating apattern for a $20 bill scanned in the forward direction derived byaveraging the patterns of FIG. 15d. This pattern becomes thecorresponding $20 master pattern after undergoing normalization. Ingenerating the master patterns, one may use a scanning device in which abill to be scanned is held stationary and a scanhead is moved over thebill. Such a device permits the scanhead to be moved laterally, left andright, over a bill to be scanned and thus permits the scanhead to bepositioned over the area of the bill which one wishes to scan, forexample, 2/10ths of inch to the left of the center of the borderlinedarea.

As discussed above, for $10 bills two patterns are obtained in each scandirection with one pattern being scanned slightly to the left of thecenter and one pattern being scanned slightly to the right of thecenter. For $5 bills, it has been found that some $5 bills are printedwith darker stairs ("dk str") on the picture of the Lincoln Memorialwhile others are printed with lighter stairs ("lt str"). The effect ofthis variance is averaged out by using an old bill having light stairsand a new bill having dark stairs.

As can be seen from Table 2, for some bills, the third method of usingold and new bills is not used; rather, a standard ("std") bill is usedfor generating all three component patterns as with the first method.Thus, the master pattern for a $1 bill scanned in the forward directionis obtained by averaging three component patterns generated by scanninga standard bill three times, once 2/10ths of an inch to the left, oncedown the center, and once 2/10ths of an inch to the right.

As illustrated by Table 2, a discrimination system may employ acombination of methods wherein, for example, some master patterns aregenerated according the first method and some master patterns aregenerated according to the third method. Likewise, a discriminationsystem may combine the scanning of new, standard, and old bills togenerate component patterns to be averaged in obtaining a masterpattern. Additionally, a discrimination system may generate masterpatterns by scanning bills of various qualities and/or having variouscharacteristics and then averaging the resultant patterns.Alternatively, a discrimination system may scan multiple bills of agiven quality for a given denomination, e.g., three new $50 bills, whilescanning one or more bills of a different quality for a differentdenomination, e.g., three old and worn $1 bills, to generate componentpatterns to be averaged in obtaining master patterns.

In order to accommodate or nullify the effect of such bill shrinking,the above-described correlation technique can be modified by use of aprogressive shifting approach whereby a test pattern which does notcorrespond to any of the master patterns is partitioned into predefinedsections, and samples in successive sections are progressively shiftedand compared again to the stored patterns in order to identify thedenomination. It has experimentally been determined that suchprogressive shifting effectively counteracts any sample displacementresulting from shrinkage of a bill along the preselected dimension.

The progressive shifting effect is best illustrated by the correlationpatterns shown in FIGS. 16a-e. For purposes of clarity, the illustratedpatterns were generated using 128 samples for each bill scan as comparedto the preferred use of 64 samples. FIG. 16a shows the correlationbetween a test pattern (represented by a heavy line) and a correspondingmaster pattern (represented by a thin line). It is clear from FIG. 16athat the degree of correlation between the two patterns is relativelylow and exhibits a correlation factor of 606.

The manner in which the correlation between these patterns is increasedby employing progressive shifting is best illustrated by considering thecorrelation at the reference points designated as A-E along the axisdefining the number of samples. The effect on correlation produced by"single" progressive shifting is shown in FIG. 16b which shows "single"shifting of the test pattern of FIG. 16a. This is effected by dividingthe test pattern into two equal segments each comprising 64 samples. Thefirst segment is retained without any shift, whereas the second segmentis shifted by a factor of one data sample. Under these conditions, it isfound that the correlation factor at the reference points located in theshifted section, particularly at point E, is improved.

FIG. 16c shows the effect produced by "double" progressive shiftingwhereby sections of the test pattern are shifted in three stages. Thisis accomplished by dividing the overall pattern into three approximatelyequal sized sections. Section one is not shifted, section two is shiftedby one data sample (as in FIG. 16b), and section three is shifted by afactor of two data samples. With "double" shifting, it can be seen thatthe correlation factor at point E is further increased.

On a similar basis, FIG. 16d shows the effect on correlation produced by"triple" progressive shifting where the overall pattern is first dividedinto four approximately equal sized sections. Subsequently, section oneis retained without any shift, section two is shifted by one datasample, section three is shifted by two data samples, and section fouris shifted by three data samples. Under these conditions, thecorrelation factor at point E is seen to have increased again.

FIG. 16e shows the effect on correlation produced by "quadruple"shifting, where the pattern is first divided into five approximatelyequal sized sections. The first four sections are shifted in accordancewith the "triple" shifting approach of FIG. 16d, whereas the fifthsection is shifted by a factor of four data samples. From FIG. 16e it isclear that the correlation at point E is increased almost to the pointof superimposition of the compared data samples.

In an alternative progressive shifting approach, the degree of shrinkageof a scanned bill is determined by comparing the length of the scannedbill, as measured by the scanhead, with the length of an "unshrunk"bill. This "unshrunk" length is pre-stored in the system memory. Thetype of progressive shifting, e.g., "single", "double", "triple", etc.,applied to the test pattern is then directly based upon the measureddegree of shrinkage. The greater the degree of shrinkage, the greaterthe number of sections into which the test pattern is divided. Anadvantage of this approach is that only one correlation factor iscalculated, as opposed to potentially calculating several correlationfactors for different types of progressive shifting.

In yet another progressive shifting approach, instead of applyingprogressive shifting to the test pattern, progressive shifting isapplied to each of the master patterns. The master patterns in thesystem memory are partitioned into predefined sections, and samples insuccessive sections are progressively shifted and compared again to thescanned test pattern in order to identify the denomination. To reducethe amount of processing time, the degree of progressive shifting whichshould be applied to the master patterns may be determined by firstmeasuring the degree of shrinkage of the scanned bill. By firstmeasuring the degree of shrinkage, only one type of progressive shiftingis applied to the stored master patterns.

Instead of rearranging the scanned test pattern or the stored masterpatterns, the system memory may contain pre-stored patternscorresponding to various types of progressive shifting. The scanned testpattern is then compared to all of these stored patterns in the systemmemory. However, to reduce the time required for processing the data,this approach may be modified to first measure the degree of shrinkageand to then select only those stored patterns from the system memorywhich correspond to the measured degree of shrinkage for comparison withthe scanned test pattern.

The advantage of using the progressive shifting approach, as opposed tomerely shifting by a set amount of data samples across the overall testpattern, is that the improvement in correlation achieved in the initialsections of the pattern as a result of shifting is not neutralized oroffset by any subsequent shifts in the test pattern. It is apparent fromthe above figures that the degree of correlation for sample pointsfalling within the progressively shifted sections increasescorrespondingly.

More importantly, the progressive shifting realizes substantialincreases in the overall correlation factor resulting from patterncomparison. For instance, the original correlation factor of 606 (FIG.16a) is increased to 681 by the "single" shifting shown in FIG. 16b. The"double" shifting shown in FIG. 16c increases the correlation number to793, the "triple" shifting of FIG. 16d increases the correlation numberto 906, and, finally, the "quadruple" shifting shown in FIG. 16eincreases the overall correlation number to 960. Using the aboveapproach, it has been determined that used currency bills which exhibita high degree of shrinkage and which cannot be accurately identified asbelonging to the correct currency denomination when the correlation isperformed without any shifting, can be identified with a high degree ofcertainty by using a progressive shifting approach, preferably byadopting "triple" or "quadruple" shifting.

The degree of correlation between a scanned pattern and a master patternmay be negatively impacted if the two patterns are not properly alignedwith each other. Such misalignment between patterns may in turnnegatively impact upon the performance of a currency identificationsystem. Misalignment between patterns may result from a number offactors. For example, if a system is designed so that the scanningprocess is initiated in response to the detection of the thin borderlinesurrounding U.S. currency or the detection of some other printed indiciasuch as the edge of printed indicia on a bill, stray marks may causeinitiation of the scanning process at an improper time. This isespecially true for stray marks in the area between the edge of a billand the edge of the printed indicia on the bill. Such stray marks maycause the scanning process to be initiated too soon, resulting in ascanned pattern which leads a corresponding master pattern.Alternatively, where the detection of the edge of a bill is used totrigger the scanning process, misalignment between patterns may resultfrom variances between the location of printed indicia on a billrelative to the edges of a bill. Such variances may result fromtolerances permitted during the printing and/or cutting processes in themanufacture of currency. For example, it has been found that location ofthe leading edge of printed indicia on Canadian currency relative to theedge of Canadian currency may vary up to approximately 0.2 inches(approximately 0.5 cm).

The problems associated with misaligned patterns may be overcome byremoving data samples from one end of a pattern to be modified andadding data values on the opposite end equal to the data valuescontained in the corresponding sequence positions of the pattern towhich the modified pattern is to be compared. This process may berepeated, up to a predetermined number of times, until a sufficientlyhigh correlation is obtained between the two patterns so as to permitthe identity of a bill under test to be called.

A preferred embodiment of the technique can be further understood byconsidering Table 3. Table 3 contains data samples generated by scanningthe narrow dimension of Canadian $2 bills along a segment positionedabout the center of the bill on the side opposite the portrait side.More specifically, the second column of Table 3 represents a scannedpattern generated by scanning a test Canadian $2 bill. The scannedpattern comprises 64 data samples arranged in a sequence. Each datasample has a sequence position, 1-64, associated therewith. The fifthcolumn represents a master pattern associated with a Canadian $2 bill.The master pattern likewise comprises a sequence of 64 data samples. Thethird and fourth columns represent the scanned pattern after it has beenmodified in the forward direction one and two times, respectively. Inthe embodiment depicted in Table 3, one data sample is removed from thebeginning of the preceding pattern during each modification.

                  TABLE 3    ______________________________________    Sequence           Scanned  Scanned Pattern                                Scanned Pattern                                          Master    Position           Pattern  Modified Once                                Modified Twice                                          Pattern    ______________________________________     1     93       50          -21       161     2     50       -21         50        100     3     -21      50          93        171     4     50       93          65        191     5     93       65          22        252     6     65       22          79        403     7     22       79          136       312     8     79       136         193       434     9     136      193         278       90    10     193      278         164       0    11     278      164         136       20    12     164      136         278       444    .      .        .           .         .    .      .        .           .         .    .      .        .           .         .    52     -490     -518        -447      -1090    53     -518     -447        -646      -767    54     -447     -646        -348      -575    55     -646     -348        -92       -514    56     -348     -92         -63       -545    57     -92      -63         -205      -40    58     -63      -205        605       1665    59     -205     605         1756      1705    60     605      1756        1401      1685    61     1756     1401        1671      2160    62     1401     1671        2154      2271    63     1671     2154        *2240     2240    64     2154     *2210       *2210     2210    ______________________________________

The modified pattern represented in the third column is generated byadding an additional data value to the end of the original scannedpattern sequence which effectively removes the first data sample of theoriginal pattern, e.g., 93, from the modified pattern. The added datavalue in the last sequence position, 64, is set equal to the data valuecontained in the 64th sequence position of the master pattern, e.g.,2210. This copying of the 64th data sample is indicated by an asteriskin the third column. The second modified pattern represented in thefourth column is generated by adding two additional data values to theend of the original scanned pattern which effectively removes the firsttwo data samples of the original scanned, e.g., 93 and 50, from thesecond modified pattern. The last two sequence positions, 63 and 64, arefilled with the data values contained in the 63rd and 64th sequencepositions of the master pattern, e.g., 2240 and 2210, respectively. Thecopying of the 63rd and 64th data samples is indicated by asterisks inthe fourth column.

In the example of Table 3, the printed area of the bill under test fromwhich the scanned pattern was generated was farther away from theleading edge of the bill than was the printed area of the bill fromwhich the master pattern was generated. As a result, the scanned patterntrailed the master pattern. The preferred embodiment of the patterngeneration method described in conjunction with Table 3 compensates forthe variance of the distance between the edge of the bill and the edgeof the printed indicia by modifying the scanned pattern in the forwarddirection. As a result of the modification method employed, thecorrelation between the original and modified versions of the scannedpattern and the master pattern increased from 705 for the original,unmodified scanned pattern to 855 for the first modified pattern and to988 for the second modified pattern. Accordingly, the bill under testwhich would otherwise have been rejected may now be properly called as agenuine $2 Canadian bill through the employment of the patterngeneration method discussed above.

Another modified discrimination technique can be understood withreference to the flowchart of FIGS. 17a-17c. The process of FIGS.17a-17c involves a method of identifying a bill under test by comparinga scanned pattern retrieved from a bill under test with one or moremaster patterns associated with one or more genuine bills. After theprocess begins at step 128a, the scanned pattern is compared with one ormore master patterns associated with genuine bills (step 128b). At step129 it is determined whether the bill under test can be identified basedon the comparison at step 128b. This may be accomplished by evaluatingthe correlation between the scanned pattern and each of the masterpatterns. If the bill can be identified, the process is ended at step130. Otherwise, one or more of the master patterns are designated forfurther processing at step 131. For example, all of the master patternsmay be designated for further processing. Alternatively, less than allof the master patterns may be designated based on a preliminaryassessment about the identity of the bill under test. For example, onlythe master patterns which had the four highest correlation values withrespect to the scanned pattern at step 128b might be chosen for furtherprocessing. In any case, the number of master patterns designated forfurther processing is M1.

At step 132, either the scanned pattern is designated for modificationor the M1 master patterns designated at step 131 are designated formodification. In a preferred embodiment, the scanned pattern isdesignated for modification and the master patterns remain unmodified.At step 133, it is designated whether forward modification or reversemodification is to be performed. This determination may be made, forexample, by analyzing the beginning or ending data samples of thescanned pattern to determine whether the scanned pattern trails or leadsthe master patterns.

At step 134, the iteration counter, I, is set equal to one. Theiteration counter is used to keep track of how many times the workingpatterns have been modified. Then at step 135, the number of incrementaldata samples, R, to be removed during each iteration is set. Forexample, only one additional data sample may be removed from eachworking pattern during each iteration in which case R is set equal toone.

At step 136, it is determined whether the scanned pattern has beendesignated for modification. If it has, then the scanned pattern isreplicated M1 times and the M1 replicated patterns, one for each of theM1 master patterns, are designated as working patterns at step 137. Ifthe scanned pattern has not been designated for modification, then theM1 master patterns have been so designated, and the M1 master patternsare replicated and designated as working patterns at step 138.Regardless of which pattern or patterns were designated formodification, at step 139, it is determined whether forward or reversemodification is to be performed on the working patterns.

If forward modification is to be performed, the first R×I data samplesfrom each working pattern are removed at step 140. The first R×I datasamples may either be explicitly removed from the working patterns or beremoved as a result of adding additional data samples (step 141) to theend of the pattern and designating the beginning of the modified patternto be the (R×I)+1 sequence position of the original pattern. As a resultof the modification, the data sample which was in the 64th sequenceposition in the original working pattern will be in the 64-(R×I)sequence position. The added data values in the last R×I sequencepositions of a working pattern are copied from the data samples in thelast R×I sequence positions of a corresponding non-designated pattern atstep 141. After the above described modification, the working patternsare compared with either respective ones of the non-designated patterns(scanned pattern modified/M1 master patterns not designated formodification) or the non-designated pattern (M1 master patternsdesignated for modification/scanned pattern not designated formodification) at step 142.

Alternatively, if reverse modification is to be performed, the last R×Idata samples from each working pattern are removed at step 143. The lastR×I data samples may either be explicitly removed from the workingpatterns or be removed as a result of adding additional data samples(step 144) to the beginning of the pattern and designating the beginningof the modified pattern to start with the added data samples. As aresult of the modification, the data sample which was in the 1stsequence position in the original working pattern will be in the (R×I)+1sequence position. The added data samples in the first R×I sequencepositions of a working pattern are copied from the data samples in thefirst R×I sequence positions of a corresponding non-designated patternat step 144. After the above described modification, the workingpatterns are compared with either respective ones of the non-designatedpatterns (scanned pattern modified/M1 master patterns not designated formodification) or the non-designated pattern (M1 master patternsdesignated for modification/scanned pattern not designated formodification) at step 142.

For example, if the scanned pattern is designated for forwardmodification and four master patterns are designated for furtherprocessing, four working patterns are generated from the scanned patternat step 137, one for each of the four master patterns. If R is set totwo at step 135, during the first iteration the last two data samplesfrom each of the M1 master patterns are copied and added to the end ofthe M1 working patterns so as to become the last two sequence positionsof the M1 working patterns, one working pattern being associated witheach of the M1 master patterns. As a result, after the first iteration,four different working patterns are generated with each working patterncorresponding to a modified version of the scanned pattern but with eachhaving data values in its last two sequence positions copied from thelast two sequence positions of a respective one of the M1 masterpatterns. After a second iteration, the last four sequence positions ofeach of the M1 master patterns are copied and added to the end of the M1working patterns so as to become the last four sequence positions of arespective one of the M1 working patterns.

As another example, if four master patterns are designated for furtherprocessing and the four designated master patterns are designated forforward modification, four working patterns are generated at step 138,one from each of the four designated master patterns. If R is set to twoat step 135, during the first iteration the last two data samples of thescanned pattern are copied and added to the end of the M1 workingpatterns so as to become the last two sequence positions of the M1working patterns, one working pattern being associated with each of theM1 master patterns. As a result, after the first iteration, fourdifferent working patterns are generated with each working patterncorresponding to a modified version of a corresponding master patternbut with each having data values in its last two sequence positioncopied from the last two sequence positions of the scanned pattern.After a second iteration, the last four sequence positions of thescanned pattern are copied and added to the end of the M1 workingpatterns so as to become the last four sequence positions of the M1working patterns.

After the comparison at step 142, it is determined whether the billunder test can be identified at step 145. If the bill can be identifiedthe process is ended at step 146. Otherwise, the iteration counter, I,is incremented by one (step 147), and the incremented iteration counteris compared to a maximum iteration number, T (step 148). If theiteration counter, I, is greater than the maximum iteration number, T,then a no call is issued (step 149a), meaning that a match sufficient toidentify the bill under test was not obtained, and the process is ended(step 149b). Otherwise, if the iteration is not greater than the maximumiteration number, the modification process is repeated beginning withstep 136.

The flowchart of FIGS. 17a-17c is intended to illustrate one preferredembodiment of the above technique. However, it is recognized that thereare numerous ways in which the steps of the flowchart of FIGS. 17a-17cmay be rearranged or altered and yet still result in the comparison ofthe same patterns as would be compared if the steps of FIGS. 17a-17cwere followed exactly. For example, instead of generating multipleworking patterns, a single working pattern may be generated and theleading or trailing sequence positions successively altered beforecomparisons to corresponding non-designated patterns. Likewise, insteadof generating multiple modified patterns directly from unmodifiedpatterns, multiple modified patterns may be generated from the precedingmodified patterns. For example, instead of generating a twice forwardmodified scanned pattern by removing the first two data samples from theoriginal scanned pattern and copying the last 2R sequence positions of acorresponding master pattern and adding these data values to the end ofthe original scanned pattern, the first data sample of the singleforward modified scanned pattern may be removed and one data sampleadded to the end of the single modified scanned pattern, and then thedata samples in the last two sequence positions may be set equal to thedata samples in the last 2R sequence positions of a corresponding masterpattern.

In a modification of the above technique, instead of copying data valuesfrom a scanned pattern into corresponding sequence positions of modifiedmaster patterns, leading or trailing sequence positions of modifiedmaster patterns are filled with zeros.

In an alternate embodiment, modified master patterns are stored, forexample in EPROM 60 of FIG. 7a, before a bill under test is scanned. Insuch an embodiment, a scanned pattern retrieved from a bill under testis compared to the modified master patterns stored in memory. Modifiedmaster patterns are generated by modifying a corresponding masterpattern in either the forward or backward direction, or both, andfilling in any trailing or leading sequence positions with zeros. Anadvantage of such a preferred embodiment is that no modification needsto be performed during the normal operation of an identification deviceincorporating such an embodiment.

An example of a procedure involved in comparing test patterns to masterpatterns is illustrated at FIG. 18a which shows the routine as startingat step 150a. At step 151a, the best and second best correlation results(referred to in FIG. 18a as the "#1 and #2 answers") are initialized tozero and, at step 152a, the test pattern is compared with each of thesixteen or eighteen original master patterns stored in the memory. Atstep 153a, the calls corresponding to the two highest correlationnumbers obtained up to that point are determined and saved. At step154a, a post-processing flag is set. At step 155a the test pattern iscompared with each of a second set of 16 or 18 master patterns stored inthe memory. This second set of master patterns is the same as the 16 or18 original master patterns except that the last sample is dropped and azero is inserted in front of the first sample. If any of the resultingcorrelation numbers is higher than the two highest numbers previouslysaved, the #1 and #2 answers are updated at step 156.

Steps 155a and 156a are repeated at steps 157a and 158a, using a thirdset of master patterns formed by dropping the last two samples from eachof the 16 original master patterns and inserting two zeros in front ofthe first sample. At steps 159a and 160a the same steps are repeatedagain, but using only $50 and $100 master patterns formed by droppingthe last three samples from the original master patterns and addingthree zeros in front of the first sample. Steps 161a and 162a repeat theprocedure once again, using only $1, $5, $10 and $20 master patternsformed by dropping the 33rd sample, whereby original samples 34-64become samples 33-63, and inserting a 0 as the new last sample. Finally,steps 163a and 164a repeat the same procedure, using master patterns for$10 and $50 bills printed in 1950, which differ significantly from billsof the same denominations printed in later years. This routine thenreturns to the main program at step 165a. The above multiple sets ofmaster patterns may be pre-stored in EPROM 60.

A modified procedure involved in comparing test patterns to green-sidemaster patterns is illustrated at FIG. 18b which shows the routine asstarting at step 150b. At step 151b, the best and second bestcorrelation results (referred to in FIG. 18b as the "#1 and #2 answers")are initialized to zero and, at step 152b, the test pattern is comparedwith each of the eighteen original green-side master patterns stored inthe memory. At step 153b, the calls corresponding to the two highestcorrelation numbers obtained up to that point are determined and saved.At step 154b, a post-processing flag is set. At step 155b the testpattern is compared with each of a second set of 18 green-side masterpatterns stored in the memory. This second set of master patterns is thesame as the 18 original green-side master patterns except that the lastsample is dropped and a zero is inserted in front of the first sample.If any of the resulting correlation numbers is higher than the twohighest numbers previously saved, the #1 and #2 answers are updated atstep 156b.

Steps 155b and 156b are repeated at steps 157b and 158b, using a thirdset of green-side master patterns formed by dropping the last twosamples from each of the 18 original master patterns and inserting twozeros in front of the first sample. At steps 159b and 160b the samesteps are repeated again, but using only $50 and $100 master patterns(two patterns for the $50 and four patterns for the $100) formed bydropping the last three samples from the original master patterns andadding three zeros in front of the first sample. Steps 161b and 162brepeat the procedure once again, using only $1, $5, $10, $20 and $50master patterns (four patterns for the $10 and two patterns for theother denominations) formed by dropping the 33rd sample whereby originalsamples 34-64 become samples 33-63, and inserting a 0 as the new lastsample. Finally, steps 163b and 164b repeat the same procedure, usingmaster patterns for $10 and $50 bills printed in 1950 (two patternsscanned along a center segment for each denomination), which differsignificantly from bills of the same denominations printed in lateryears. This routine then returns to the main program at step 165b. Theabove multiple sets of master patterns may be pre-stored in EPROM 60.

In another modified embodiment where conditional black-side correlationis to be performed, a modified version of the routine designated as"CORRES" is initiated. The procedure involved in executing the modifiedversion of CORRES is illustrated at FIG. 19a, which shows the routine asstarting at step 180. Step 181 determines whether the bill has beenidentified as a $2 bill, and, if the answer is negative, step 182determines whether the best correlation number ("call #1") is greaterthan 799. If the answer is negative, the correlation number is too lowto identify the denomination of the bill with certainty, and at step183b a black side correlation routine is called (described in moredetail below in conjunction with FIGS. 19b-19c).

An affirmative answer at step 182 advances the system to step 186, whichdetermines whether the sample data passes an ink stain test (describedbelow). If the answer is negative, a "no call" bit is set in acorrelation result flag at step 183a. A "no call previous bill" flag isthen set at step 184, and the routine returns to the main program atstep 185. If the answer at step 186 is affirmative, the system advancesto step 187 which determines whether the best correlation number isgreater than 849. An affirmative answer at step 187 indicates that thecorrelation number is sufficiently high that the denomination of thescanned bill can be identified with certainty without any furtherchecking. Consequently, a "good call" bit is set in the correlationresult flag at step 188. A separate register associated with the bestcorrelation number (#1) may then be used to identify the denominationrepresented by the stored pattern resulting in the highest correlationnumber. The system returns to the main program at step 185.

A negative answer at step 187 indicates that the correlation number isbetween 800 and 850. It has been found that correlation numbers withinthis range are sufficient to identify all bills except the $2 bill.Accordingly, a negative response at step 187 advances the system to step189 which determines whether the difference between the two highestcorrelation numbers ("call #1" and "call #2") is greater than 149. Ifthe answer is affirmative, the denomination identified by the highestcorrelation number is acceptable, and thus the "good call" bit is set inthe correlation result flag at step 188. If the difference between thetwo highest correlation numbers is less than 150, step 189 produces anegative response which advances the system to step 183b where the blackside correlation routine is called.

Returning to step 181, an affirmative response at this step indicatesthat the initial call is a $2 bill. This affirmative response initiatesa series of steps 190-193 which are similar to steps 182, 186, 187 and189 described above, except that the numbers 799 and 849 used in steps182 and 187 are changed to 849 and 899, respectively, in steps 190 and192. The result is either the setting of a "no call" bit in acorrelation result flag at step 183a, the setting of the "good call" bitin the correlation result flag at step 188, or the calling of the blackside correlation routine at step 183b.

Turning now to FIGS. 19b and 19c there is shown a flowchart illustratingthe steps of the black side correlation routine called at step 183b ofFIG. 19a. After the black side correlation routine is initiated at step600, it is determined at step 602 whether the lower read head was theread head that scanned the black side of the test bill. If it was, thelower read head data is normalized at step 604. Otherwise, it isdetermined at step 606 whether the upper read head was the read headthat scanned the black side of the test bill. If it was, the upper readhead data is normalized at step 608. If it cannot be determined whichread head scanned the black side of the bill, then the patternsgenerated from both sides of the test bill are correlated against thegreen-side master patterns (see, e.g., step 110 of FIG. 12). Under sucha circumstance, the "no call" bit in the correlation result flag is setat step 610, the "no call previous bill" flag is set at step 611, andthe program returns to the calling point at step 612.

After the lower read head data is normalized at step 604, or the upperread head data is normalized at step 608, it is determined whether thebest green-side correlation number is greater than 700 at step 614. Anegative response at step 614 results in the "no call" bit in thecorrelation result flag being set at step 610, the "no call previousbill" flag being set at step 611, and the program returning to thecalling point at step 612. An affirmative response at step 614 resultsin a determination being made as to whether the best call from the greenside correlation corresponds to a $20, $50, or $100 bill at step 616. Anegative response at step 616 results in the "no call" bit in thecorrelation result flag being set at step 610, the "no call previousbill" flag being set at step 611, and the program returning to thecalling point at step 612.

If it is determined at step 616 that the best call from the green sidecorrelation corresponds to a $20, $50, or $100 bill, the scanned patternfrom the black side is correlated against the black-side master patternsassociated with the specific denomination and scan direction associatedwith the best call from the green side. According to a preferredembodiment, multiple black-side master patterns are stored for $20, $50and $100 bills. For each of these denominations, three master patternsare stored for scans in the forward direction, and three master patternsare stored for scans in the reverse direction, for a total of sixpatterns for each denomination. For a given scan direction, black-sidemaster patterns are generated by scanning a corresponding denominatedbill along a segment located about the center of the narrow dimension ofthe bill, a segment slightly displaced (0.2 inches) to the left ofcenter, and a segment slightly displaced (0.2 inches) to the right ofcenter.

For example, at step 618, it is determined whether the best call fromthe green side is associated with a forward scan of a $20 bill and, ifit is, the normalized data from the black side of the test bill iscorrelated against the black-side master patterns associated with aforward scan of a $20 bill at step 620. Next it is determined whetherthe black-side correlation number is greater than 900 at step 622. If itis, the "good call" bit in the correlation result flag is set at step648, and the program returns to the calling point at step 646. If theblack-side correlation number is not greater than 900, then the "no callbit" in the correlation result flag is set at step 642, the "no callprevious bill" flag is set at step 644, and the program returns to thecalling point at step 646. If it is determined that the best call fromthe green side is not associated with a forward scan of $20 bill at step618, the program branches accordingly at steps 624-640 so that thenormalized data from the black side of the test bill is correlatedagainst the appropriate black-side master patterns.

The mechanical portions of the currency scanning and counting module areshown in FIGS. 20a-22. From the input receptacle, the bills are moved inseriatim from the bottom of the stack along a curved guideway 211 whichreceives bills moving downwardly and rearwardly and changes thedirection of travel to a forward direction. The curvature of theguideway 211 corresponds substantially to the curved periphery of thedrive roll 223 so as to form a narrow passageway for the bills along therear side of the drive roll. The exit end of the guideway 211 directsthe bills onto a linear path where the bills are scanned. The bills aretransported with the narrow dimension of the bills maintained parallelto the transport path and the direction of movement at all times.

Bills that are stacked on the bottom wall 205 of the input receptacleare stripped, one at a time, from the bottom of the stack. The bills arestripped by a pair of stripping wheels 220 mounted on a drive shaft 221which, in turn, is supported across side plates 201, 202. The strippingwheels 220 project through a pair of slots formed in a cover 207. Partof the periphery of each wheel 220 is provided with a raisedhigh-friction, serrated surface 222 which engages the bottom bill of theinput stack as the wheels 220 rotate, to initiate feeding movement ofthe bottom bill from the stack. The serrated surfaces 222 projectradially beyond the rest of the wheel peripheries so that the wheels"jog" the bill stack during each revolution so as to agitate and loosenthe bottom currency bill within the stack, thereby facilitating thestripping of the bottom bill from the stack.

The stripping wheels 220 feed each stripped bill B (FIG. 21a) onto adrive roll 223 mounted on a driven shaft 224 supported across the sideplates 201 and 202. As can be seen most clearly in FIGS. 21a and 21b,the drive roll 223 includes a central smooth friction surface 225 formedof a material such as rubber or hard plastic. This smooth frictionsurface 225 is sandwiched between a pair of grooved surfaces 226 and 227having serrated portions 228 and 229 formed from a high-frictionmaterial.

The serrated surfaces 228, 229 engage each bill after it is fed onto thedrive roll 223 by the stripping wheels 220, to frictionally advance thebill into the narrow arcuate passageway formed by the curved guideway211 adjacent the rear side of the drive roll 223. The rotationalmovement of the drive roll 223 and the stripping wheels 220 issynchronized so that the serrated surfaces on the drive roll and thestripping wheels maintain a constant relationship to each other.Moreover, the drive roll 223 is dimensioned so that the circumference ofthe outermost portions of the grooved surfaces is greater than the widthW of a bill, so that the bills advanced by the drive roll 223 are spacedapart from each other. That is, each bill fed to the drive roll 223 isadvanced by that roll only when the serrated surfaces 228, 229 come intoengagement with the bill, so that the circumference of the drive roll223 determines the spacing between the leading edges of successivebills.

To avoid the simultaneous removal of multiple bills from the stack inthe input receptacle, particularly when small stacks of bills are loadedinto the machine, the stripping wheels 220 are always stopped with theraised, serrated portions 222 positioned below the bottom wall 205 ofthe input receptacle. This is accomplished by continuously monitoringthe angular position of the serrated portions of the stripping wheels220 via the encoder 32, and then controlling the stopping time of thedrive motor so that the motor always stops the stripping wheels in aposition where the serrated portions 222 are located beneath the bottomwall 205 of the input receptacle. Thus, each time a new stack of billsis loaded into the machine, those bills will rest on the smooth portionsof the stripping wheels. This has been found to significantly reduce thesimultaneous feeding of double or triple bills, particularly when smallstacks of bills are involved.

In order to ensure firm engagement between the drive roll 223 and thecurrency bill being fed, an idler roll 230 urges each incoming billagainst the smooth central surface 225 of the drive roll 223. The idlerroll 230 is journalled on a pair of arms 231 which are pivotally mountedon a support shaft 232. Also mounted on the shaft 232, on opposite sidesof the idler roll 230, are a pair of grooved guide wheels 233 and 234.The grooves in these two wheels 233, 234 are registered with the centralribs in the two grooved surfaces 226, 227 of the drive roll 223. Thewheels 233, 234 are locked to the shaft 232, which in turn is lockedagainst movement in the direction of the bill movement (clockwise asviewed in FIG. 20a) by a one-way spring clutch 235. Each time a bill isfed into the nip between the guide wheels 233, 234 and the drive roll223, the clutch 235 is energized to turn the shaft 232 just a fewdegrees in a direction opposite the direction of bill movement. Theserepeated incremental movements distribute the wear uniformly around thecircumferences of the guide wheels 233, 234. Although the idler roll 230and the guide wheels 233, 234 are mounted behind the guideway 211, theguideway is apertured to allow the roll 230 and the wheels 233, 234 toengage the bills on the front side of the guideway.

Beneath the idler roll 230, a spring-loaded pressure roll 236 (FIGS. 20aand 21b) presses the bills into firm engagement with the smooth frictionsurface 225 of the drive roll as the bills curve downwardly along theguideway 211. This pressure roll 236 is journalled on a pair of arms 237pivoted on a stationary shaft 238. A spring 239 attached to the lowerends of the arms 237 urges the roll 236 against the drive roll 233,through an aperture in the curved guideway 211.

At the lower end of the curved guideway 211, the bill being transportedby the drive roll 223 engages a flat guide plate 240 which carries alower scan head 18. Currency bills are positively driven along the flatplate 240 by means of a transport roll arrangement which includes thedrive roll 223 at one end of the plate and a smaller driven roll 241 atthe other end of the plate. Both the driver roll 223 and the smallerroll 241 include pairs of smooth raised cylindrical surfaces 242 and 243which hold the bill flat against the plate 240. A pair of O rings 244and 245 fit into grooves formed in both the roll 241 and the roll 223 toengage the bill continuously between the two rolls 223 and 241 totransport the bill while helping to hold the bill flat against the guideplate 240.

The flat guide plate 240 is provided with openings through which theraised surfaces 242 and 243 of both the drive roll 223 and the smallerdriven roll 241 are subjected to counter-rotating contact withcorresponding pairs of passive transport rolls 250 and 251 havinghigh-friction rubber surfaces. The passive rolls 250, 251 are mounted onthe underside of the flat plate 240 in such a manner as to befreewheeling about their axes 254 and 255 and biased intocounter-rotating contact with the corresponding upper rolls 223 and 241.The passive rolls 250 and 251 are biased into contact with the drivenrolls 223 and 241 by means of a pair of H-shaped leaf springs 252 and253 (see FIGS. 23 and 24). Each of the four rolls 250, 251 is cradledbetween a pair of parallel arms of one of the H-shaped leaf springs 252and 253. The central portion of each leaf spring is fastened to theplate 240, which is fastened rigidly to the machine frame, so that therelatively stiff arms of the H-shaped springs exert a constant biasingpressure against the rolls and push them against the upper rolls 223 and241.

The points of contact between the driven and passive transport rolls arepreferably coplanar with the flat upper surface of the plate 240 so thatcurrency bills can be positively driven along the top surface of theplate in a flat manner. The distance between the axes of the two driventransport rolls, and the corresponding counter-rotating passive rolls,is selected to be just short of the length of the most narrow dimensionof the currency bills. Accordingly, the bills are firmly gripped underuniform pressure between the upper and lower transport rolls within thescanhead area, thereby minimizing the possibility of bill skew andenhancing the reliability of the overall scanning and recognitionprocess.

The positive guiding arrangement described above is advantageous in thatuniform guiding pressure is maintained on the bills as they aretransported through the optical scanhead area, and twisting or skewingof the bills is substantially reduced. This positive action issupplemented by the use of the H-springs 252, 253 for uniformly biasingthe passive rollers into contact with the active rollers so that billtwisting or skew resulting from differential pressure applied to thebills along the transport path is avoided. The O-rings 244, 245 functionas simple, yet extremely effective means for ensuring that the centralportions of the bills are held flat.

The location of a magnetic head 256 and a magnetic head adjustment screw257 are illustrated in FIG. 23. The adjustment screw 257 adjusts theproximity of the magnetic head 256 relative to a passing bill andthereby adjusts the strength of the magnetic field in the vicinity ofthe bill.

FIG. 22 shows the mechanical arrangement for driving the various meansfor transporting currency bills through the machine. A motor 260 drivesa shaft 261 carrying a pair of pulleys 262 and 263. The pulley 262drives the roll 241 through a belt 264 and pulley 265, and the pulley263 drives the roll 223 through a belt 266 and pulley 267. Both pulleys265 and 267 are larger than pulleys 262 and 263 in order to achieve thedesired speed reduction from the typically high speed at which the motor260 operates.

The shaft 221 of the stripping wheels 220 is driven by means of a pulley268 provided thereon and linked to a corresponding pulley 269 on theshaft 224 through a belt 270. The pulleys 268 and 269 are of the samediameter so that the shafts 221 and 224 rotate in unison.

As shown in FIG. 20b, the optical encoder 32 is mounted on the shaft ofthe roller 241 for precisely tracking the position of each bill as it istransported through the machine, as discussed in detail above inconnection with the optical sensing and correlation technique.

The upper and lower scanhead assemblies are shown most clearly in FIGS.25-28. It can be seen that the housing for each scanhead is formed as anintegral part of a unitary molded plastic support member 280 or 281 thatalso forms the housings for the light sources and photodetectors of thephotosensors PS1 and PS2. The lower member 281 also forms the flat guideplate 240 that receives the bills from the drive roll 223 and supportsthe bills as they are driven past the scanheads 18a and 18b.

The two support members 280 and 281 are mounted facing each other sothat the lenses 282 and 283 of the two scanheads 18a, 18b define anarrow gap through which each bill is transported. Similar, but slightlylarger, gaps are formed by the opposed lenses of the light sources andphotodetectors of the photosensors PS1 and PS2. The upper support member280 includes a tapered entry guide 280a which guides an incoming billinto the gaps between the various pairs of opposed lenses.

The lower support member 281 is attached rigidly to the machine frame.The upper support member 280, however, is mounted for limited verticalmovement when it is lifted manually by a handle 284, to facilitate theclearing of any paper jams that occur beneath the member 280. To allowfor such vertical movement, the member 280 is slidably mounted on a pairof posts 285 and 286 on the machine frame, with a pair of springs 287and 288 biasing the member 280 to its lowermost position.

Each of the two optical scanheads 18a and 18b housed in the supportmembers 280, 281 includes a pair of light sources acting in combinationto uniformly illuminate light strips of the desired dimension onopposite sides of a bill as it is transported across the plate 240.Thus, the upper scanhead 18a includes a pair of LEDs 22a, directinglight downwardly through an optical mask on top of the lens 282 onto abill traversing the flat guide plate 240 beneath the scanhead. The LEDs22a are angularly disposed relative to the vertical axis of the scanheadso that their respective light beams combine to illuminate the desiredlight strip defined by an aperture in the mask. The scanhead 18a alsoincludes a photodetector 26a mounted directly over the center of theilluminated strip for sensing the light reflected off the strip. Thephotodetector 26a is linked to the CPU 30 through the ADC 28 forprocessing the sensed data as described above.

When the photodetector 26a is positioned on an axis passing through thecenter of the illuminated strip, the illumination by the LED's as afunction of the distance from the central point "0" along the X axis,should optimally approximate a step function as illustrated by the curveA in FIG. 29. With the use of a single light source angularly displacedrelative to a vertical axis through the center of the illuminated strip,the variation in illumination by an LED typically approximates aGaussian function, as illustrated by the curve B in FIG. 29.

The two LEDs 22a are angularly disposed relative to the vertical axis byangles α and β, respectively. The angles α and β are selected to be suchthat the resultant strip illumination by the LED's is as close aspossible to the optimum distribution curve A in FIG. 29. The LEDillumination distribution realized by this arrangement is illustrated bythe curve designated as "C" in FIG. 29 which effectively merges theindividual Gaussian distributions of each light source to yield acomposite distribution which sufficiently approximates the optimum curveA.

In the particular embodiment of the scanheads 18a and 18b illustrated inthe drawings, each scanhead includes two pairs of LEDs and twophotodetectors for illuminating, and detecting light reflected from,strips of two different sizes. Thus, each mask also includes two slitswhich are formed to allow light from the LEDs to pass through andilluminate light strips of the desired dimensions. More specifically,one slit illuminates a relatively wide strip used for obtaining thereflectance samples which correspond to the characteristic pattern for atest bill. In a preferred embodiment, the wide slit has a length ofabout 0.500" and a width of about 0.050". The second slit forms arelatively narrow illuminated strip used for detecting the thinborderline surrounding the printed indicia on currency bills, asdescribed above in detail. In a preferred embodiment, the narrow slit283 has a length of about 0.300" and a width of about 0.010".

In order to prevent dust from fouling the operation of the scanheads,each scanhead includes three resilient seals or gaskets 290, 291, and292. The two side seals 290 and 291 seal the outer ends of the LEDs 22,while the center seal 292 seals the outer end of the photodetector 26.Thus, dust cannot collect on either the light sources or thephotodetectors, and cannot accumulate and block the slits through whichlight is transmitted from the sources to the bill, and from the bill tothe photodetectors.

Doubling or overlapping of bills in the illustrative transport system isdetected by two photosensors PS1 and PS2 which are located on a commontransverse axis that is perpendicular to the direction of bill flow (seee.g., FIGS. 30a and 30b). The photosensors PS1 and PS2 includephotodetectors 293 and 294 mounted within the lower support member 281in immediate opposition to corresponding light sources 295 and 296mounted in the upper support member 280. The photodetectors 293, 294detect beams of light directed downwardly onto the bill transport pathfrom the light sources 295, 296 and generate analog outputs whichcorrespond to the sensed light passing through the bill. Each suchoutput is converted into a digital signal by a conventional ADCconvertor unit (not shown) whose output is fed as a digital input to andprocessed by the system CPU.

The presence of a bill adjacent the photosensors PS1 and PS2 causes achange in the intensity of the detected light, and the correspondingchanges in the analog outputs of the photodetectors 293 and 294 serve asa convenient means for density-based measurements for detecting thepresence of "doubles" (two or more overlaid or overlapped bills) duringthe currency scanning process. For instance, the photosensors may beused to collect a predefined number of density measurements on a testbill, and the average density value for a bill may be compared topredetermined density thresholds (based, for instance, on standardizeddensity readings for master bills) to determine the presence of overlaidbills or doubles.

In order to prevent the accumulation of dirt on the light sources 295and 296 and/or the photodetectors 293, 294 of the photosensors PS1 andPS2, both the light sources and the photodetectors are enclosed bylenses mounted so close to the bill path that they are continually wipedby the bills. This provides a self-cleaning action which reducesmaintenance problems and improves the reliability of the outputs fromthe photosensors over long periods of operation.

The CPU 30, under control of software stored in the EPROM 34, monitorsand controls the speed at which the bill transport mechanism 16transports bills from the bill separating station 14 to the billstacking unit. Flowcharts of the speed control routines stored in theEPROM 34 are depicted in FIGS. 31-35. To execute more than the firststep in any given routine, the currency discriminating system 10 must beoperating in a mode requiring the execution of the routine.

Referring first to FIG. 31, when a user places a stack of bills in thebill accepting station 12 for counting, the transport speed of the billtransport mechanism 16 must accelerate or "ramp up" from zero to topspeed. Therefore, in response to receiving the stack of bills in thebill accepting station 12, the CPU 30 sets a ramp-up bit in a motor flagstored in the memory unit 38. Setting the ramp-up bit causes the CPU 30to proceed beyond step 300b of the ramp-up routine. If the ramp-up bitis set, the CPU 30 utilizes a ramp-up counter and a fixed parameter"ramp-up step" to incrementally increase the transport speed of the billtransport mechanism 16 until the bill transport mechanism 16 reaches itstop speed. The "ramp-up step" is equal to the incremental increase inthe transport speed of the bill transport mechanism 16, and the ramp-upcounter determines the amount of time between incremental increases inthe bill transport speed. The greater the value of the "ramp-up step",the greater the increase in the transport speed of the bill transportmechanism 16 at each increment. The greater the maximum value of theramp-up counter, the greater the amount of time between increments.Thus, the greater the value of the "ramp-up step" and the lesser themaximum value of the ramp-up counter, the lesser the time it takes thebill transport mechanism 16 to reach its top speed.

The ramp-up routine in FIG. 31 employs a variable parameter "new speed",a fixed parameter "full speed", and the variable parameter "transportspeed". The "full speed" represents the top speed of the bill transportmechanism 16, while the "new speed" and "transport speed" represent thedesired current speed of the bill transport mechanism 16. To account foroperating offsets of the bill transport mechanism 16, the "transportspeed" of the bill transport mechanism 16 actually differs from the "newspeed" by a "speed offset value". Outputting the "transport speed" tothe bill transport mechanism 16 causes the bill transport mechanism 16to operate at the transport speed.

To incrementally increase the speed of the bill transport mechanism 16,the CPU 30 first decrements the ramp-up counter from its maximum value(step 301). If the maximum value of the ramp-up counter is greater thanone at step 302, the CPU 30 exits the speed control software in FIGS.31-35 and repeats steps 300b, 301, and 302 during subsequent iterationsof the ramp-up routine until the ramp-up counter is equal to zero. Whenthe ramp-up counter is equal to zero, the CPU 30 resets the ramp-upcounter to its maximum value (step 303). Next, the CPU 30 increases the"new speed" by the "ramp-up step" (step 304). If the "new speed" is notyet equal to the "full speed" at step 305, the "transport speed" is setequal to the "new speed" plus the "speed offset value" (step 306). The"transport speed" is output to the bill transport mechanism 16 at step307 of the routine in FIG. 31 to change the speed of the bill transportmechanism 16 to the "transport speed". During subsequent iterations ofthe ramp-up routine, the CPU 30 repeats steps 300b-306 until the "newspeed" is greater than or equal to the "full speed".

Once the "new speed" is greater than or equal to the "full speed" atstep 305, the ramp-up bit in the motor flag is cleared (step 308), apause-after-ramp bit in the motor flag is set (step 309), apause-after-ramp counter is set to its maximum value (step 310), and theparameter "new speed" is set equal to the "full speed" (step 311).Finally, the "transport speed" is set equal to the "new speed" plus the"speed offset value" (step 306). Since the "new speed" is equal to the"full speed", outputting the "transport speed" to the bill transportmechanism 16 causes the bill transport mechanism 16 to operate at itstop speed. The ramp-up routine in FIG. 31 smoothly increases the speedof the bill transport mechanism without causing jerking or motor spikes.Motor spikes could cause false triggering of the optical scanhead 18such that the scanhead 18 scans non-existent bills.

During normal counting, the bill transport mechanism 16 transports billsfrom the bill separating station 14 to the bill stacking unit at its topspeed. In response to the optical scanhead 18 detecting a stranger,suspect or no call bill, however, the CPU 30 sets a ramp-to-slow-speedbit in the motor flag. Setting the ramp-to-slow-speed bit causes the CPU30 to proceed beyond step 312 of the ramp-to-slow-speed routine in FIG.32 on the next iteration of the software in FIGS. 31-35. Using theramp-to-slow-speed routine in FIG. 32, the CPU 30 causes the billtransport mechanism 16 to controllably decelerate or "ramp down" fromits top speed to a slow speed. As the ramp-to-slow speed routine in FIG.32 is similar to the ramp-up routine in FIG. 31, it is not described indetail herein.

It suffices to state that if the ramp-to-slow-speed bit is set in themotor flag, the CPU 30 decrements a ramp-down counter (step 313) anddetermines whether or not the ramp-down counter is equal to zero (step314). If the ramp-down counter is not equal to zero, the CPU 30 exitsthe speed control software in FIGS. 31-35 and repeats steps 312, 313,and 314 of the ramp-to-slow-speed routine in FIG. 32 during subsequentiterations of the speed control software until the ramp-down counter isequal to zero. Once the ramp-down counter is equal to zero, the CPU 30resets the ramp-down counter to its maximum value (step 315) andsubtracts a "ramp-down step" from the variable parameter "new speed"(step 316). The "new speed" is equal to the fixed parameter "full speed"prior to initiating the ramp-to-slow-speed routine in FIG. 32.

After subtracting the "ramp-down step" from the "new speed", the "newspeed" is compared to a fixed parameter "slow speed" (step 317). If the"new speed" is greater than the "slow speed", the "transport speed" isset equal to the "new speed" plus the "speed offset value" (step 318)and this "transport speed" is output to the bill transport mechanism 16(step 307 of FIG. 31). During subsequent iterations of theramp-to-slow-speed routine, the CPU 30 continues to decrement the "newspeed" by the "ramp-down step" until the "new speed" is less than orequal to the "slow speed". Once the "new speed" is less than or equal tothe "slow speed" at step 317, the CPU 30 clears the ramp-to-slow-speedbit in the motor flag (step 319), sets the pause-after-ramp bit in themotor flag (step 320), sets the pause-after-ramp counter (step 321), andsets the "new speed" equal to the "slow speed" (step 322). Finally, the"transport speed" is set equal to the "new speed" plus the "speed offsetvalue" (step 318). Since the "new speed" is equal to the "slow speed",outputting the "transport speed" to the bill transport mechanism 16causes the bill transport mechanism 16 to operate at its slow speed. Theramp-to-slow-speed routine in FIG. 32 smoothly decreases the speed ofthe bill transport mechanism 16 without causing jerking or motor spikes.

FIG. 33 depicts a ramp-to-zero-speed routine in which the CPU 30 rampsdown the transport speed of the bill transport mechanism 16 to zeroeither from its top speed or its slow speed. In response to completionof counting of a stack of bills, the CPU 30 enters this routine to rampdown the transport speed of the bill transport mechanism 16 from its topspeed to zero. Similarly, in response to the optical scanhead 18detecting a stranger, suspect, or no call bill and theramp-to-slow-speed routine in FIG. 32 causing the transport speed to beequal to a slow speed, the CPU 30 enters the ramp-to-zero-speed routineto ramp down the transport speed from the slow speed to zero.

With the ramp-to-zero-speed bit set at step 323, the CPU 30 determineswhether or not an initial-braking bit is set in the motor flag (step324). Prior to ramping down the transport speed of the bill transportmechanism 16, the initial-braking bit is clear. Therefore, flow proceedsto the left branch of the ramp-to-zero-speed routine in FIG. 33. In thisleft branch, the CPU 30 sets the initial-braking bit in the motor flag(step 325), resets the ramp-down counter to its maximum value (step326), and subtracts an "initial-braking step" from the variableparameter "new speed" (step 327). Next, the CPU 30 determines whether ornot the "new speed" is greater than zero (step 328). If the "new speed"is greater than zero at step 328, the variable parameter "transportspeed" is set equal to the "new speed" plus the "speed offset value"(step 329) and this "transport speed" is output to the bill transportmechanism 16 at step 307 in FIG. 31.

During the next iteration of the ramp-to-zero-speed routine in FIG. 33,the CPU 30 enters the right branch of the routine at step 324 becausethe initial-braking bit was set during the previous iteration of theramp-to-zero-speed routine. With the initial-braking bit set, the CPU 30decrements the ramp-down counter from its maximum value (step 330) anddetermines whether or not the ramp-down counter is equal to zero (step331). If the ramp-down counter is not equal to zero, the CPU 30immediately exits the speed control software in FIGS. 31-35 and repeatssteps 323, 324, 330, and 331 of the ramp-to-slow-speed routine duringsubsequent iterations of the speed control software until the ramp-downcounter is equal to zero. Once the ramp-down counter is equal to zero,the CPU 30 resets the ramp-down counter to its maximum value (step 332)and subtracts a "ramp-down step" from the variable parameter "new speed"(step 333). This "ramp-down step" is smaller than the "initial-brakingstep" so that the "initial-braking step" causes a larger decrementalchange in the transport speed of the bill transport mechanism 16 thanthat caused by the "ramp-down step".

Next, the CPU 30 determines whether or not the "new speed" is greaterthan zero (step 328). If the "new speed" is greater than zero, the"transport speed" is set equal to the "new speed" plus the "speed offsetvalue" (step 329) and this "transport speed" is outputted to the billtransport mechanism 16 (step 307 in FIG. 31). During subsequentiterations of the speed control software, the CPU 30 continues todecrement the "new speed" by the "ramp-down step" at step 333 until the"new speed" is less than or equal to zero at step 328. Once the "newspeed" is less than or equal to the zero at step 328, the CPU 30 clearsthe ramp-to-zero-speed bit and the initial-braking bit in the motor flag(step 334), sets a motor-at-rest bit in the motor flag (step 335), andsets the "new speed" equal to zero (step 336). Finally, the "transportspeed" is set equal to the "new speed" plus the "speed offset value"(step 329). Since the "new speed" is equal to zero, outputting the"transport speed" to the bill transport mechanism 16 at step 307 in FIG.31 halts the bill transport mechanism 16.

Using the feedback loop routine in FIG. 35, the CPU 30 monitors andstabilizes the transport speed of the bill transport mechanism 16 whenthe bill transport mechanism 16 is operating at its top speed or at slowspeed. To measure the transport speed of the bill transport mechanism16, the CPU 30 monitors the optical encoder 32. While monitoring theoptical encoder 32, it is important to synchronize the feedback looproutine with any transport speed changes of the bill transport mechanism16. To account for the time lag between execution of the ramp-up orramp-to-slow-speed routines in FIGS. 31-32 and the actual change in thetransport speed of the bill transport mechanism 16, the CPU 30 enters apause-after-ramp routine in FIG. 34 prior to entering the feedback looproutine in FIG. 35 if the bill transport mechanism 16 completed rampingup to its top speed or ramping down to slow speed during the previousiteration of the speed control software in FIGS. 31-35.

The pause-after-ramp routine in FIG. 34 allows the bill transportmechanism 16 to "catch up" to the CPU 30 so that the CPU 30 does notenter the feedback loop routine in FIG. 35 prior to the bill transportmechanism 16 changing speeds. As stated previously, the CPU 30 sets apause-after-ramp bit during step 309 of the ramp-up routine in FIG. 31or step 320 of the ramp-to-slow-speed routine in FIG. 32. With thepause-after-ramp bit set, flow proceeds from step 337 of thepause-after-ramp routine to step 338, where the CPU 30 decrements apause-after-ramp counter from its maximum value. If the pause-after-rampcounter is not equal to zero at step 339, the CPU 30 exits thepause-after-ramp routine in FIG. 34 and repeats steps 337, 338, and 339of the pause-after-ramp routine during subsequent iterations of thespeed control software until the pause-after-ramp counter is equal tozero. Once the pause-after-ramp counter decrements to zero, the CPU 30clears the pause-after-ramp bit in the motor flag (step 340) and setsthe feedback loop counter to its maximum value (step 341). The maximumvalue of the pause-after-ramp counter is selected to delay the CPU 30 byan amount of time sufficient to permit the bill transport mechanism 16to adjust to a new transport speed prior to the CPU 30 monitoring thenew transport speed with the feedback loop routine in FIG. 35.

Referring now to the feedback loop routine in FIG. 35, if themotor-at-rest bit in the motor flag is not set at step 342, the CPU 30decrements a feedback loop counter from its maximum value (step 343). Ifthe feedback loop counter is not equal to zero at step 344, the CPU 30immediately exits the feedback loop routine in FIG. 35 and repeats steps342, 343, and 344 of the feedback loop routine during subsequentiterations of the speed control software in FIGS. 31-36 until thefeedback loop counter is equal to zero. Once the feedback loop counteris decremented to zero, the CPU 30 resets the feedback loop counter toits maximum value (step 345), stores the present count of the opticalencoder 32 (step 346), and calculates a variable parameter "actualdifference" between the present count and a previous count of theoptical encoder 32 (step 347). The "actual difference" between thepresent and previous encoder counts represents the transport speed ofthe bill transport mechanism 16. The larger the "actual difference"between the present and previous encoder counts, the greater thetransport speed of the bill transport mechanism. The CPU 30 subtractsthe "actual difference" from a fixed parameter "requested difference" toobtain a variable parameter "speed difference" (step 348).

If the "speed difference" is greater than zero at step 349, the billtransport speed of the bill transport mechanism 16 is too slow. Tocounteract slower than ideal bill transport speeds, the CPU 30multiplies the "speed difference" by a "gain constant" (step 354) andsets the variable parameter "transport speed" equal to the multiplieddifference from step 354 plus the "speed offset value" plus a fixedparameter "target speed" (step 355). The "target speed" is a value that,when added to the "speed offset value", produces the ideal transportspeed. The calculated "transport speed" is greater than this idealtransport speed by the amount of the multiplied difference. If thecalculated "transport speed" is nonetheless less than or equal to afixed parameter "maximum allowable speed" at step 356, the calculated"transport speed" is output to the bill transport mechanism 16 at step307 so that the bill transport mechanism 16 operates at the calculated"transport speed". If, however, the calculated "transport speed" isgreater than the "maximum allowable speed" at step 356, the parameter"transport speed" is set equal to the "maximum allowable speed" (step357) and is output to the bill transport mechanism 16 (step 307).

If the "speed difference" is less than or equal to zero at step 349, thebill transport speed of the bill transport mechanism 16 is too fast oris ideal. To counteract faster than ideal bill transport speeds, the CPU30 multiplies the "speed difference" by a "gain constant" (step 350) andsets the variable parameter "transport speed" equal to the multiplieddifference from step 350 plus the "speed offset value" plus a fixedparameter "target speed" (step 351). The calculated "transport speed" isless than this ideal transport speed by the amount of the multiplieddifference. If the calculated "transport speed" is nonetheless greaterthan or equal to a fixed parameter "minimum allowable speed" at step352, the calculated "transport speed" is output to the bill transportmechanism 16 at step 307 so that the bill transport mechanism 16operates at the calculated "transport speed". If, however, thecalculated "transport speed" is less than the "minimum allowable speed"at step 352, the parameter "transport speed" is set equal to the"minimum allowable speed" (step 353) and is output to the bill transportmechanism 16 (step 307).

It should be apparent that the smaller the value of the "gain constant",the smaller the variations of the bill transport speed betweensuccessive iterations of the feedback control routine in FIG. 35 and,accordingly, the less quickly the bill transport speed is adjustedtoward the ideal transport speed. Despite these slower adjustments inthe bill transport speed, it is generally preferred to use a relativelysmall "gain constant" to prevent abrupt fluctuations in the billtransport speed and to prevent overshooting the ideal bill transportspeed.

A routine for using the outputs of the two photosensors PS1 and PS2 todetect any doubling or overlapping of bills is illustrated in FIG. 36 bysensing the optical density of each bill as it is scanned. This routinestarts at step 401 and retrieves the denomination determined for thepreviously scanned bill at step 402. This previously determineddenomination is used for detecting doubles in the event that the newlyscanned bill is a "no call", as described below. Step 403 determineswhether the current bill is a "no call," and if the answer is negative,the denomination determined for the new bill is retrieved at step 404.

If the answer at step 403 is affirmative, the system jumps to step 405,so that the previous denomination retrieved at step 402 is used insubsequent steps. To permit variations in the sensitivity of the densitymeasurement, a "density setting" is retrieved from memory at step 405.If the "density setting" has been turned off, this condition is sensedat step 406, and the system returns to the main program at step 413. Ifthe "density setting" is not turned off, a denominational densitycomparison value is retrieved from memory at step 407.

The memory preferably contains five different density values (for fivedifferent density settings, i.e., degrees of sensitivity) for eachdenomination. Thus, for a currency set containing seven differentdenominations, the memory contains 35 different values. The denominationretrieved at step 404 (or step 402 in the event of a "no call"), and thedensity setting retrieved st step 405, determine which of the 35 storedvalues is retrieved at step 407 for use in the comparison stepsdescribed below.

At step 408, the density comparison value retrieved at step 407 iscompared to the average density represented by the output of thephotosensor PS1. The result of this comparison is evaluated at step 409to determine whether the output of sensor S1 identifies a doubling ofbills for the particular denomination of bill determined at step 402 or404. If the answer is negative, the system returns to the main programat step 413. If the answer is affirmative, step 410 then compares theretrieved density comparison value to the average density represented bythe output of the second sensor PS2. The result of this comparison isevaluated at step 411 to determine whether the output of the photosensorPS2 identifies a doubling of bills. Affirmative answers at both step 409and step 411 result in the setting of a "doubles error" flag at step412, and the system then returns to the main program at step 413. The"doubles error" flag can, of course, be used to stop the bill transportmotor.

FIG. 37 illustrates a routine that enables the system to detect billswhich have been badly defaced by dark marks such as ink blotches,felt-tip pen marks and the like. Such severe defacing of a bill canresult in such distorted scan data that the data can be interpreted toindicate the wrong denomination for the bill. Consequently, it isdesirable to detect such severely defaced bills and then stop the billtransport mechanism so that the bill in question can be examined by theoperator.

The routine of FIG. 37 retrieves each successive data sample at step450b and then advances to step 451 to determine whether that sample istoo dark. As described above, the output voltage from the photodetector26 decreases as the darkness of the scanned area increases. Thus, thelower the output voltage from the photodetector, the darker the scannedarea. For the evaluation carried out at step 451, a preselectedthreshold level for the photodetector output voltage, such as athreshold level of about 1 volt, is used to designate a sample that is"too dark."

An affirmative answer at step 451 advances the system to step 452 wherea "bad sample" count is incremented by one. A single sample that is toodark is not enough to designate the bill as seriously defaced. Thus, the"bad sample" count is used to determine when a preselected number ofconsecutive samples, e.g., ten consecutive samples, are determined to betoo dark. From step 452, the system advances to step 453 to determinewhether ten consecutive bad samples have been received. If the answer isaffirmative, the system advances to step 454 where an error flag is set.This represents a "no call" condition, which causes the bill transportsystem to be stopped in the same manner discussed above.

When a negative response is obtained at step 451, the system advances tostep 455 where the "bad sample" count is reset to zero, so that thiscount always represents the number of consecutive bad samples received.From step 455 the system advances to step 456 which determines when allthe samples for a given bill have been checked. As long as step 456yields a negative answer, the system continues to retrieve successivesamples at step 450b. When an affirmative answer is produced at step456, the system returns to the main program at step 457.

A routine for automatically monitoring and making any necessarycorrections in various line voltages is illustrated in FIG. 38. Thisroutine is useful in automatically compensating for voltage drifts dueto temperature changes, aging of components and the like. The routinestarts at step 550 and reads the output of a line sensor which ismonitoring a selected voltage at step 550b. Step 551 determines whetherthe reading is below 0.60, and if the answer is affirmative, step 552determines whether the reading is above 0.40. If step 552 also producesan affirmative response, the voltage is within the required range andthus the system returns to the main program step 553. If step 551produces a negative response, an incremental correction is made at step554 to reduce the voltage in an attempt to return it to the desiredrange. Similarly, if a negative response is obtained at step 552, anincremental correction is made at step 555 to increase the voltagetoward the desired range.

Because currencies come in a variety of sizes, sensors may be added todetermine the size of a bill to be scanned. These sensors are placedupstream of the scanheads. A preferred embodiment of size determiningsensors is illustrated in FIG. 39. Two leading/trailing edge sensors1062 detect the leading and trailing edges of a bill 1064 as it passesalong the transport path. These sensors in conjunction with the encoder32 (FIGS. 2a-2b) may be used to determine the dimension of the billalong a direction parallel to the scan direction which in FIG. 39 is thenarrow dimension (or width) of the bill 1064. Additionally, two sideedge sensors 1066 are used to detect the dimension of a bill 1064transverse to the scan direction which in FIG. 39 is the wide dimension(or length) of the bill 1064. While the sensors 1062 and 1066 of FIG. 39are optical sensors, other means of determining the size of a bill maybe employed.

Once the size of a bill is determined, the potential identity of thebill is limited to those bills having the same size. Accordingly, thearea to be scanned can be tailored to the area or areas best suited foridentifying the denomination and country of origin of a bill having themeasured dimensions.

While the printed indicia on U.S. currency is enclosed within a thinborderline, the sensing of which may serve as a trigger to beginscanning using a wider slit, most currencies of other currency systemssuch as those from other countries do not have such a borderline. Thusthe system described above may be modified to begin scanning relative tothe edge of a bill for currencies lacking such a borderline. Referringto FIG. 40, two leading edge detectors 1068 are shown. The detection ofthe leading edge 1069 of a bill 1070 by leading edge sensors 1068triggers scanning in an area a given distance away from the leading edgeof the bill 1070, e.g., D₁ or D₂, which may vary depending upon thepreliminary indication of the identity of a bill based on the dimensionsof a bill. Alternatively, the leading edge 1069 of a bill may bedetected by one or more of the scanheads (to be described below) in asimilar manner as that described with respect to FIGS. 7a and 7b.Alternatively, the beginning of scanning may be triggered by positionalinformation provided by the encoder 32 of FIGS. 2a-2b, for example, inconjunction with the signals provided by sensors 1062 of FIG. 39, thuseliminating the need for leading edge sensors 1068.

However, when the initiation of scanning is triggered by the detectionof the leading edge of a bill, the chance that a scanned pattern will beoffset relative to a corresponding master pattern increases. Offsets canresult from the existence of manufacturing tolerances which permit thelocation of printed indicia of a document to vary relative to the edgesof the document. For example, the printed indicia on U.S. bills may varyrelative to the leading edge of a bill by as much as 50 mils which is0.05 inches (1.27 mm). Thus when scanning is triggered relative to theedge of a bill (rather than the detection of a certain part of theprinted indicia itself, such as the printed borderline of U.S. bills), ascanned pattern can be offset from a corresponding master pattern by oneor more samples. Such offsets can lead to erroneous rejections ofgenuine bills due to poor correlation between scanned and masterpatterns. To compensate, overall scanned patterns and master patternscan be shifted relative to each other as illustrated in FIGS. 41a and41b. More particularly, FIG. 41a illustrates a scanned pattern which isoffset from a corresponding master pattern. FIG. 41b illustrates thesame patterns after the scanned pattern is shifted relative to themaster pattern, thereby increasing the correlation between the twopatterns. Alternatively, instead of shifting either scanned patterns ormaster patterns, master patterns may be stored in memory correspondingto different offset amounts.

Thirdly, while it has been determined that the scanning of the centralarea on the green side of a U.S. bill (see segment S of FIG. 4) providessufficiently distinct patterns to enable discrimination among theplurality of U.S. denominations, the central area may not be suitablefor bills originating in other countries. For example, for billsoriginating from Country 1, it may be determined that segment S₁ (FIG.40) provides a more preferable area to be scanned, while segment S₂(FIG. 40) is more preferable for bills originating from Country 2.Alternatively, in order to sufficiently discriminate among a given setof bills, it may be necessary to scan bills which are potentially fromsuch set along more than one segment, e.g., scanning a single bill alongboth S₁ and S₂. To accommodate scanning in areas other than the centralportion of a bill, multiple scanheads may be positioned next to eachother. A preferred embodiment of such a multiple scanhead system isdepicted in FIG. 42. Multiple scanheads 1072a-c and 1072d-f arepositioned next to each other along a direction lateral to the directionof bill movement. Such a system permits a bill 1074 to be scanned alongdifferent segments. Multiple scanheads 1072a-f are arranged on each sideof the transport path, thus permitting both sides of a bill 1074 to bescanned.

Two-sided scanning may be used to permit bills to be fed into a currencydiscrimination system according to the present invention with eitherside face up. An example of a two-sided scanhead arrangement isdescribed above in connection with FIGS. 2a, 6c, and 6d. Master patternsgenerated by scanning genuine bills may be stored for segments on one orboth sides. In the case where master patterns are stored from thescanning of only one side of a genuine bill, the patterns retrieved byscanning both sides of a bill under test may be compared to a master setof single-sided master patterns. In such a case, a pattern retrievedfrom one side of a bill under test should match one of the stored masterpatterns, while a pattern retrieved from the other side of the billunder test should not match one of the master patterns. Alternatively,master patterns may be stored for both sides of genuine bills. In such atwo-sided system, a pattern retrieved by scanning one side of a billunder test should match with one of the master patterns of one side(Match 1) and a pattern retrieved from scanning the opposite side of abill under test should match the master pattern associated with theopposite side of a genuine bill identified by Match 1.

Alternatively, in situations where the face orientation of a bill (i.e.,whether a bill is "face up" or "face down") may be determined prior toor during characteristic pattern scanning, the number of comparisons maybe reduced by limiting comparisons to patterns corresponding to the sameside of a bill. That is, for example, when it is known that a bill is"face up", scanned patterns associated with scanheads above thetransport path need only be compared to master patterns generated byscanning the "face" of genuine bills. By "face" of a bill it is meant aside which is designated as the front surface of the bill. For example,the front or "face" of a U.S. bill may be designated as the "black"surface while the back of a U.S. bill may be designated as the "green"surface. The face orientation may be determinable in some situations bysensing the color of the surfaces of a bill. An alternative method ofdetermining the face orientation of U.S. bills by detecting theborderline on each side of a bill is described above in connection withFIGS. 6c, 6d, and 12. The implementation of color sensing is discussedin more detailed below.

According to the embodiment of FIG. 42, the bill transport mechanismoperates in such a fashion that the central area C of a bill 1074 istransported between central scanheads 1072b and 1072e. Scanheads 1072aand 1072c and likewise scanheads 1072d and 1072f are displaced the samedistance from central scanheads 1072b and 1072e, respectively. Bysymmetrically arranging the scanheads about the central region of abill, a bill may be scanned in either direction, e.g., top edge first(forward direction) or bottom edge first (reverse direction). Asdescribed above with respect to FIGS. 1-7b, master patterns are storedfrom the scanning of genuine bills in both the forward and reversedirections. While a symmetrical arrangement is preferred, it is notessential provided appropriate master patterns are stored for anon-symmetrical system.

While FIG. 42 illustrates a system having three scanheads per side, anynumber of scanheads per side may be utilized. Likewise, it is notnecessary that there be a scanhead positioned over the central region ofa bill. For example, FIG. 43 illustrates another preferred embodiment ofthe present invention capable of scanning the segments S₁ and S₂ of FIG.40. Scanheads 1076a, 1076d, 1076e, and 1076h scan a bill 1078 alongsegment S₁ while scanheads 1076b, 1076c, 1076f, and 1076g scan segmentS₂.

FIG. 44 depicts another preferred embodiment of a scanning systemaccording to the present invention having laterally moveable scanheads1080a-b. Similar scanheads may be positioned on the opposite side of thetransport path. Moveable scanheads 1080a-b may provide more flexibilitythat may be desirable in certain scanning situations. Upon thedetermination of the dimensions of a bill as described in connectionwith FIG. 39, a preliminary determination of the identity of a bill maybe made. Based on this preliminary determination, the moveable scanheads1080a-b may be positioned over the area of the bill which is mostappropriate for retrieving discrimination information. For example, ifbased on the size of a scanned bill, it is preliminarily determined thatthe bill is a Japanese 5000 Yen bill-type, and if it has been determinedthat a suitable characteristic pattern for a 5000 Yen bill-type isobtained by scanning a segment 2.0 cm to the left of center of the billfed in the forward direction, scanheads 1080a and 1080b may beappropriately positioned for scanning such a segment, e.g., scanhead1080a positioned 2.0 cm left of center and scanhead 1080b positioned 2.0cm right of center. Such positioning permits proper discriminationregardless of the whether the scanned bill is being fed in the forwardor reverse direction. Likewise scanheads on the opposite side of thetransport path (not shown) could be appropriately positioned.Alternatively, a single moveable scanhead may be used on one or bothsides of the transport path. In such a system, size and colorinformation (to be described in more detail below) may be used toproperly position a single laterally moveable scanhead, especially wherethe orientation of a bill may be determined before scanning.

FIG. 44 depicts a system in which the transport mechanism is designed todeliver a bill 1082 to be scanned centered within the area in whichscanheads 1080a-b are located. Accordingly, scanheads 1080a-b aredesigned to move relative to the center of the transport path withscanhead 1080a being moveable within the range R₁ and scanhead 1080bbeing moveable within range R₂.

FIG. 45 depicts another preferred embodiment of a scanning systemaccording to the present invention wherein bills to be scanned aretransported in a left justified manner along the transport path, that iswherein the left edge L of a bill 1084 is positioned in the same laterallocation relative to the transport path. Based on the dimensions of thebill, the position of the center of the bill may be determined and thescanheads 1086a-b may in turn be positioned accordingly. As depicted inFIG. 45, scanhead 1086a has a range of motion R₃ and scanhead 1086b hasa range of motion R₄. The ranges of motion of scanheads 1086a-b may beinfluenced by the range of dimensions of bills which the discriminationsystem is designed to accommodate. Similar scanheads may be positionedon the opposite side of the transport path.

Alternatively, the transport mechanism may be designed such that scannedbills are not necessarily centered or justified along the lateraldimension of the transport path. Rather the design of the transportmechanism may permit the position of bills to vary left and right withinthe lateral dimension of the transport path. In such a case, the edgesensors 1066 of FIG. 39 may be used to locate the edges and center of abill, and thus provide positional information in a moveable scanheadsystem and selection criteria in a stationary scanhead system.

In addition to the stationary scanhead and moveable scanhead systemsdescribed above, a hybrid system having both stationary and moveablescanheads may be used. Likewise, it should be noted that the laterallydisplaced scanheads described above need not lie along the same lateralaxis. That is, the scanheads may be, for example, staggered upstream anddownstream from each other. FIG. 46 is a top view of a staggeredscanhead arrangement according to a preferred embodiment of the presentinvention. As illustrated in FIG. 46, a bill 1130 is transported in acentered manner along the transport path 1132 so that the center 1134 ofthe bill 1130 is aligned with the center 1136 of the transport path1132. Scanheads 1140a-h are arranged in a staggered manner so as topermit scanning of the entire width of the transport path 1132. Theareas illuminated by each scanhead are illustrated by strips 1142a,1142b, 1142e, and 1142f for scanheads 1140a, 1140b, 1140e, and 1140f,respectively. Based on size determination sensors, scanheads 1140a and1140h may either not be activated or their output ignored.

In general, if prior to scanning a document, preliminary informationabout a document can be obtained, such as its size or color,appropriately positioned stationary scanheads may be activated orlaterally moveable scanheads may be appropriately positioned providedthe preliminary information provides some indication as to the potentialidentity of the document. Alternatively, especially in systems havingscanheads positioned over a significant portion of the transport path,many or all of the scanheads of a system may be activated to scan adocument. Then subsequently, after some preliminary determination as toa document's identity has been made, only the output or derivationsthereof of appropriately located scanheads may be used to generatescanned patterns. Derivations of output signals include, for example,data samples stored in memory generated by sampling output signals.Under such an alternative embodiment, information enabling a preliminarydetermination as to a document's identity may be obtained by analyzinginformation either from sensors separate from the scanheads or from oneor more of the scanheads themselves. An advantage of such preliminarydeterminations is that the number of scanned patterns which have to begenerated or compared to a set of master patterns is reduced. Likewisethe number of master patterns to which scanned patterns must be comparedmay also be reduced.

While the scanheads 1140a-h of FIG. 46 are arranged in a non-overlappingmanner, they may alternatively be arranged in an overlapping manner. Byproviding additional lateral positions, an overlapping scanheadarrangement may provide greater selectivity in the segments to bescanned. This increase in scanable segments may be beneficial incompensating for currency manufacturing tolerances which result inpositional variances of the printed indicia on bills relative to theiredges. Additionally, in a preferred embodiment, scanheads positionedabove the transport path are positioned upstream relative to theircorresponding scanheads positioned below the transport path.

FIGS. 47a and 47b illustrate another embodiment wherein a plurality ofanalog sensors 1150 such as photodetectors are laterally displaced fromeach other and are arranged in a linear array within a single scanhead1152. FIG. 47a is a top view while FIG. 47b is a side elevation view ofsuch a linear array embodiment. The output of individual sensors 1150are connected to photodetectors (not shown) through the use of gradedindex fibers, such as a "lens array" manufactured by MSG America, Inc.,part number SLA20A1675702A3, and subsequently to analog-to-digitalconverters and a CPU (not shown) in a manner similar to that depicted inFIGS. 1 and 6a. As depicted in FIGS. 47a and 47b, a bill 1154 istransported past the linear array scanhead 1152 in a centered fashion. Apreferred length for the linear array scanhead is about 6-7 inches (15cm-17 cm).

In a manner similar to that described above, based on the determinationof the size of a bill, appropriate sensors may be activated and theiroutput used to generate scanned patterns. Alternatively many or all ofthe sensors may be activated with only the output or derivations thereofof appropriately located sensors being used to generate scannedpatterns. Derivations of output signals include, for example, datasamples stored in memory generated by sampling output signals. As aresult, a discriminating system incorporating a linear array scanheadaccording the present invention would be capable of accommodating a widevariety of bill-types. Additionally, a linear array scanhead provides agreat deal of flexibility in how information may be read and processedwith respect to various bills. In addition to the ability to generatescanned patterns along segments in a direction parallel to the directionof bill movement, by appropriately processing scanned samples, scannedpatterns may be "generated" or approximated in a direction perpendicularto the direction of bill movement. For example, if the linear arrayscanhead 1152 comprises one hundred and sixty (160) sensors 1150 over alength of 7 inches (17.78 cm) instead of taking samples for 64 encoderpulses from say 30 sensors, samples may be taken for 5 encoder pulsesfrom all 160 cells (or all those positioned over the bill 1154).Alternatively, 160 scanned patterns (or selected ones thereof) of 5 datasamples each may be used for pattern comparisons. Accordingly, it can beseen that the data acquisition time is significantly reduced from 64encoder pulses to only 5 encoder pulses. The time saved in acquiringdata can be used to permit more time to be spent processing data and/orto reduce the total scanning time per bill thus enabling increasedthroughput of the identification system. Additionally, the linear arrayscanhead permits a great deal of flexibility in tailoring the areas tobe scanned. For example, it has been found that the leading edges ofCanadian bills contain valuable graphic information. Accordingly, whenit is determined that a test bill may be a Canadian bill (or when theidentification system is set to a Canadian currency setting), thescanning area can be limited to the leading edge area of bills, forexample, by activating many laterally displaced sensors for a relativelysmall number of encoder pulses.

FIG. 48 is a top view of another preferred embodiment of a linear arrayscanhead 1170 having a plurality of analog sensors 1172 such asphotodetectors wherein a bill 1174 is transported past the scanhead 1170in a non-centered manner. As discussed above, positional informationfrom size-determining sensors may be used to select appropriate sensors.Alternatively, the linear array scanhead itself may be employed todetermine the size of a bill, thus eliminating the need for separatesize-determining sensors. For example, all sensors may be activated,data samples derived from sensors located on the ends of the lineararray scanhead may be preliminarily processed to determine the lateralposition and the length of a bill. The width of a bill may be determinedeither by employing separate leading/trailing edge sensors orpre-processing data samples derived from initial and ending cycleencoder pulses. Once size information is obtained about a bill undertest, only the data samples retrieved from appropriate areas of a billneed be further processed.

FIG. 49 is a top view of another embodiment of a linear scanhead 1180having the ability to compensate for skewing of bills. Scanhead 1180 hasa plurality of analog sensors 1182 and a bill 1184 is transported pastscanhead 1180 in a skewed manner. Once the skew of a bill has beendetermined, for example through the use of leading edge sensors,readings from sensors 1182 along the scanhead 1180 may be appropriatelydelayed. For example, suppose it is determined that a bill is being fedpast scanhead 1180 so that the left front corner of the bill reaches thescanhead five encoder pulses before the right front corner of the bill.In such a case, sensor readings along the right edge of the bill can bedelayed for 5 encoder pulses to compensate for the skew. Where scannedpatterns are to be generated over only a few encoder pulses, the billmay be treated as being fed in a non-skewed manner since the amount oflateral deviation between a scan along a skewed angle and a scan along anon-skewed angle is minimal for a scan of only a few encoder pulses.However, where it is desired to obtain a scan over a large number ofencoder pulses, a single scanned pattern may be generated from theoutputs of more than one sensor. For example, a scanned pattern may begenerated by taking data samples from sensor 1186a for a given number ofencoder pulses, then taking data samples from sensor 1186b for a nextgiven number of encoder pulses, and then taking data samples from sensor1186c for a next given number of encoder pulses. The number of givenencoder pulses for which data samples may be taken from the same sensoris influenced by the degree of skew: the greater the degree of skew ofthe bill, the fewer the number of data samples which may be obtainedbefore switching to the next sensor. Alternatively, master patterns maybe generated and stored for various degrees of skew, thus permitting asingle sensor to generate a scanned pattern from a bill under test.

With regard to FIGS. 47-49, while only a single linear array scanhead isshown, another linear array scanhead may be positioned on the oppositeside of the transport path to permit scanning of either or both sides ofa bill. Likewise, the benefits of using a linear array scanhead may alsobe obtainable using a multiple scanhead arrangement which is configuredappropriately, such as depicted in FIG. 46 or a linear arrangement ofmultiple scanheads.

In addition to size and scanned characteristic patterns, color may alsobe used to discriminate bills. For example, while all U.S. bills areprinted in the same colors, e.g., a green side and a black side, billsfrom other countries often vary in color with the denomination of thebill. For example, a German 50 deutsche mark bill is brown in colorwhile a German 100 deutsche mark bill is blue in color. Alternatively,color detection may be used to determine the face orientation of a bill,such as where the color of each side of a bill varies. For example,color detection may be used to determine the face orientation of U.S.bills by detecting whether or not the "green" side of a U.S. bill isfacing upwards. Separate color sensors may be added upstream of thescanheads described above. According to such an embodiment, colorinformation may be used in addition to size information to preliminarilyidentify a bill. Likewise, color information may be used to determinethe face orientation of a bill, which determination may be used toselect upper or lower scanheads for scanning a bill, or to comparescanned patterns retrieved from upper scanheads with a set of masterpatterns generated by scanning a corresponding face while the scannedpatterns retrieved from the lower scanheads are compared with a set ofmaster patterns generated by scanning an opposing face. Alternatively,color sensing may be incorporated into the scanheads described above.Such color sensing may be achieved by, for example, incorporating colorfilters, colored light sources, and/or dichroic beamsplitters into thecurrency discrimination system of the present invention. Colorinformation acquisition is described in more detail in co-pending U.S.application Ser. No. 08/219,093 filed Mar. 29, 1994, for a "CurrencyDiscriminator and Authenticator", incorporated herein by reference.Various color information acquisition techniques are described in U.S.Pat. Nos. 4,841,358; 4,658,289; 4,716,456; 4,825,246; and 4,992,860.

The operation of a currency discriminator according to one preferredembodiment may be further understood by referring to the flowchart ofFIGS. 50a and 50b. In the process beginning at step 1100, a bill is fedalong a transport path (step 1102) past sensors which measure the lengthand width of the bill (step 1104). These size determining sensors maybe, for example, those illustrated in FIG. 39. Next at step 1106, it isdetermined whether the measured dimensions of the bill match thedimensions of at least one bill stored in memory, such as EPROM 60 ofFIG. 7a. If no match is found, an appropriate error is generated at step1108. If a match is found, the color of the bill is scanned at step1110. At step 1112, it is determined whether the color of the billmatches a color associated with a genuine bill having the dimensionsmeasured at step 1104. An error is generated at step 1114 if no suchmatch is found. However, if a match is found, a preliminary set ofpotentially matching bills is generated at step 1116. Often, only onepossible identity will exist for a bill having a given color anddimensions. However, the preliminary set of step 1116 is not limited tothe identification of a single bill-type, that is, a specificdenomination of a specific currency system; but rather, the preliminaryset may comprise a number of potential bill-types. For example, all U.S.bills have the same size and color. Therefore, the preliminary setgenerated by scanning a U.S. $5 bill would include U.S. bills of alldenominations.

Based on the preliminary set (step 1116), selected scanheads in astationary scanhead system may be activated (step 1118). For example, ifthe preliminary identification indicates that a bill being scanned hasthe color and dimensions of a German 100 deutsche mark bill, thescanheads over regions associated with the scanning of an appropriatesegment for a German 100 deutsche mark bill may be activated. Then upondetection of the leading edge of the bill by sensors 1068 of FIG. 40,the appropriate segment may be scanned. Alternatively, all scanheads maybe active with only the scanning information from selected scanheadsbeing processed. Alternatively, based on the preliminary identificationof a bill (step 1116), moveable scanheads may be appropriatelypositioned (step 1118).

Subsequently, the bill is scanned for a characteristic pattern (step1120). At step 1122, the scanned patterns produced by the scanheads arecompared with the stored master patterns associated with genuine billsas dictated by the preliminary set. By only making comparisons withmaster patterns of bills within the preliminary set, processing time maybe reduced. Thus for example, if the preliminary set indicated that thescanned bill could only possibly be a German 100 deutsche mark bill,then only the master pattern or patterns associated with a German 100deutsche mark bill need be compared to the scanned patterns. If no matchis found, an appropriate error is generated (step 1124). If a scannedpattern does match an appropriate master pattern, the identity of thebill is accordingly indicated (step 1126) and the process is ended (step1128).

While some of the embodiments discussed above entail a system capable ofidentifying a plurality of bill-types, the system may be adapted toidentify a bill under test as either belonging to a specific bill-typeor not. For example, the system may be adapted to store masterinformation associated with only a single bill-type such as a UnitedKingdom 5 pound bill. Such a system would identify bills under testwhich were United Kingdom 5 pound bills and would reject all otherbill-types.

The scanheads described above may be incorporated into a currencyidentification system capable of identifying a variety of currencies.For example, the system may be designed to accommodate a number ofcurrencies from different countries. Such a system may be designed topermit operation in a number of modes. For example, the system may bedesigned to permit an operator to select one or more of a plurality ofbill-types which the system is designed to accommodate. Such a selectionmay be used to limit the number of master patterns with which scannedpatterns are to be compared. Likewise, the operator may be permitted toselect the manner in which bills will be fed, such as all bills face up,all bills top edge first, random face orientation, and/or random topedge orientation. Additionally, the system may be designed to permitoutput information to be displayed in a variety of formats to a varietyof output devices, such as a monitor, LCD display, or printer. Forexample, the system may be designed to count the number of each specificbill-type identified and to tabulate the total amount of currencycounted for each of a plurality of currency systems. For example, astack of bills could be placed in the bill accepting station 12 of FIGS.2a-2b, and the output unit 36 of FIGS. 2a-2b may indicate that a totalof 370 British pounds and 650 German marks were counted. Alternatively,the output from scanning the same batch of bills may provide moredetailed information about the specific denominations counted, forexample, one 100 pound bill, five 50 pound bills, and one 20 pound billand thirteen 50 deutsche mark bills.

In a currency identification system capable of identifying a variety ofbills from a number of countries, a manual selection device, such as aswitch or a scrolling selection display, may be provided so that thecustomer may designate what type of currency is to be discriminated. Forexample, in a system designed to accommodate both Canadian and Germancurrency, the customer could turn a dial to the Canadian bill setting orscroll through a displayed menu and designate Canadian bills. Bypre-declaring what type of currency is to be discriminated, scannedpatterns need only be compared to master patterns corresponding to theindicated type of currency, e.g., Canadian bills. By reducing the numberof master patterns which have to be compared to scanned patterns, theprocessing time can be reduced.

Alternatively, a system may be designed to compare scanned patterns toall stored master patterns. In such a system, the customer need notpre-declare what type of currency is to be scanned. This reduces thedemands on the customer. Furthermore, such a system would permit theinputting of a mixture of bills from a number of countries. The systemwould scan each bill and automatically determine the issuing country andthe denomination.

In addition to the manual and automatic bill-type discriminatingsystems, an alternate system employs a semi-automatic bill-typediscriminating method. Such a system operates in a manner similar to thestranger mode described above. In such a system, a stack of bills isplaced in the input hopper. The first bill is scanned and the generatedscanned pattern is compared with the master patterns associated withbills from a number of different countries. The discriminator identifiesthe country-type and the denomination of the bill. Then thediscriminator compares all subsequent bills in the stack to the masterpatterns associated with bills only from the same country as the firstbill. For example, if a stack of U.S. bills were placed in the inputhopper and the first bill was a $5 bill, the first bill would bescanned. The scanned pattern would be compared to master patternsassociated with bills from a number of countries, e.g., U.S., Canadian,and German bills. Upon determining that the first bill is a U.S. $5bill, scanned patterns from the remaining bills in the stack arecompared only to master patterns associated with U.S. bills, e.g., $1,$2, $5, $10, $20, $50, and $100 bills. When a bill fails to sufficientlymatch one of the compared patterns, the bill may be flagged as describedabove such as by stopping the transport mechanism while the flagged billis returned to the customer.

A currency discriminating device designed to accommodate both Canadianand German currency bills will now be described. According to thisembodiment, a currency discriminating device similar to that describedabove in connection with scanning U.S. currency (see, e.g., FIGS. 1-38and accompanying description) is modified so as to be able to acceptboth Canadian and German currency bills. According to a preferredembodiment when Canadian bills are being discriminated, no magneticsampling or authentication is performed.

Canadian bills have one side with a portrait (the portrait side) and areverse side with a picture (the picture side). Likewise, German billsalso have one side with a portrait (the portrait side) and a reverseside with a picture (the picture side). In a preferred embodiment, thediscriminator is designed to accept either stacks of Canadian bills orstacks of German bills, the bills in the stacks being faced so that thepicture side of all the bills will be scanned by a triple scanheadarrangement to be described in connection with FIG. 51. In a preferredembodiment, this triple scanhead replaces the single scanheadarrangement housed in the unitary molded plastic support member 280(see, e.g., FIGS. 25 and 26).

FIG. 51 is a top view of a triple scanhead arrangement 1200. The triplescanhead arrangement 1200 comprises a center scanhead 1202, a leftscanhead 1204, and a right scanhead 1206 housed in a unitary moldedplastic support member 1208. A bill 1210 passes under the arrangement1200 in the direction shown. O-rings are positioned near each scanhead,preferably two O-rings per scanhead, one on each side of a respectivescanhead, to engage the bill continuously while transporting the billbetween rolls 223 and 241 (FIG. 20a) and to help hold the bill flatagainst the guide plate 240 (FIG. 20a). The left 1204 and right 1206scanhead are placed slightly upstream of the center scanhead 1202 by adistance D₃. In a preferred embodiment, D₃ is 0.083 inches (0.21 cm).The center scanhead 1202 is centered over the center C of the transportpath 1216. The center L_(C) of the left scanhead 1204 and the centerR_(C) of the right scanhead 1206 are displaced laterally from center Cof the transport path in a symmetrical fashion by a distance D₄. In apreferred embodiment, D₄ is 1.625 inches (4.128 cm).

The scanheads 1202, 1204, and 1206 are each similar to the scanheadsdescribed above connection with FIGS. 1-38, except only a wide slithaving a length of about 0.500 inch and a width of about 0.050 inch isutilized. The wide slit of each scanhead is used both to detect theleading edge of a bill and to scan a bill after the leading edge hasbeen detected.

Two photosensors 1212 and 1214 are located along the lateral axis of theleft and right scanheads 1204 and 1206, one on either side of the centerscanhead 1202. Photosensors 1212 and 1214 are same as the photosensorsPS1 and PS2 described above (see, e.g., FIGS. 26 and 30). Photosensors1212 and 1214 are used to detect doubles and also to measure thedimensions of bills in the direction of bill movement which in thepreferred embodiment depicted in FIG. 51 is the narrow dimension ofbills. Photosensors 1212 and 1214 are used to measure the narrowdimension of a bill by indicating when the leading and trailing edges ofa bill passes by the photosensors 1212 and 1214. This information incombination with the encoder information permits the narrow dimension ofa bill to be measured.

All Canadian bills are 6 inches (15.24 cm) in their long dimension and2.75 inches (6.985 cm) in their narrow dimension. German bills vary insize according to denomination. In a preferred embodiment of thecurrency discriminating system, the discriminating device is designed toaccept and discriminate $2, $5, $10, $20, $50, and $100 Canadian billsand 10 DM, 20 DM, 50 DM, and 100 DM German bills. These German billsvary in size from 13.0 cm (5.12 inches) in the long dimension by 6.0 cm(2.36 inches) in the narrow dimension for 10 DM bills to 16.0 cm (6.30inches) in the long dimension by 8.0 cm (3.15 inches) in the narrowdimension for 100 DM bills. The input hopper of the discriminatingdevice is made sufficiently wide to accommodate all the above listedCanadian and German bills, e.g., 6.3 inches (16.0 cm) wide.

FIG. 52 is a top view of a Canadian bill illustrating the areas scannedby the triple scanhead arrangement of FIG. 51. In generating scannedpatterns from a Canadian bill 1300 traveling along a transport path1301, segments SL₁, SC₁, and SR₁ are scanned by the left 1204, center1202, and right 1206 scanheads, respectively, on the picture side of thebill 1300. These segments are similar to segment S in FIG. 4. Eachsegment begins a predetermined distance D₅ inboard of the leading edgeof the bill. In a preferred embodiment D₅ is 0.5" (1.27 cm). SegmentsSL₁, SC₁, and SR₁ each comprise 64 samples as shown in FIGS. 3 and 5. Ina preferred embodiment Canadian bills are scanned at a rate of 1000bills per minute. The lateral location of segments SL₁, SC₁, and SR₁ isfixed relative to the transport path 1301 but may vary left to rightrelative to bill 1300 since the lateral position of bill 1300 may varyleft to right within the transport path 1301.

A set of eighteen master Canadian patterns are stored for each type ofCanadian bill that the system is designed to discriminate, three foreach scanhead in both the forward and reverse directions. For example,three patterns are generated by scanning a given genuine Canadian billin the forward direction with the center scanhead. One pattern isgenerated by scanning down the center of the bill along segment SC₁, asecond is generated by scanning along a segment SC₂ initiated 1.5samples before the beginning of SC₁, and a third is generated byscanning along a segment SC₃ initiated 1.5 samples after the beginningof SC₁. The second and third patterns are generated to compensate forthe problems associated with triggering off the edge of a bill asdiscussed above.

To compensate for possible lateral displacement of bills to be scannedalong a direction transverse to the direction of bill movement, theexact lateral location along which each of the above master patterns isgenerated is chosen after considering the correlation results achievedwhen a bill is displaced slightly to the left or to the right of thecenter of each scanhead, i.e., lines L_(C), S_(C), and R_(C). Forexample, in generating a master pattern associated with segment SC₁, ascan of a genuine bill may be taken down the center of a bill, a secondscan may be taken along a segment 0.15 inch to the right of center(+0.15 inch), and a third scan may be taken along a segment 0.15 inch tothe left of center (-0.15 inch). Based on the correlation resultachieved, the actual scan location may be adjusted slightly to the rightor left so the effect of the lateral displacement of a bill on thecorrelation results is minimized. Thus, for example, the master patternassociated with a forward scan of a Canadian $2 bill using the centerscanhead 1202 may be taken along a line 0.05 inch to the right of thecenter of the bill.

Furthermore, the above stored master patterns are generated either byscanning both a relatively new crisp genuine bill and an older yellowedgenuine bill and averaging the patterns generated from each or,alternatively, by scanning an average looking bill.

Master patterns are stored for nine types of Canadian bills, namely, thenewer series $2, $5, $10, $20, $50, and $100 bills and the older series$20, $50, and $100 bills. Accordingly, a total of 162 Canadian masterpatterns are stored (9 types×18 per type).

FIG. 53 is a flowchart of the threshold test utilized in calling thedenomination of a Canadian bill. When Canadian bills are beingdiscriminated the flowchart of FIG. 53 replaces the flowchart of FIG.13. The correlation results associated with correlating a scannedpattern to a master pattern of a given type of Canadian bill in a givenscan direction and a given offset in the direction of bill movement fromeach of the three scanheads are summed. The highest of the resulting 54summations is designated the #1 correlation and the second highest ispreliminarily designated the #2 correlation. The #1 and #2 correlationseach have a given bill type associated with them. If the bill typeassociated with the #2 correlation is merely a different series from,but the same denomination as, the bill type associated with the #1denomination, the preliminarily designated #2 correlation is substitutedwith the next highest correlation where the bill denomination isdifferent from the denomination of the bill type associated with the #1correlation.

The threshold test of FIG. 53 begins at step 1302. Step 1304 checks thedenomination associated with the #1 correlation. If the denominationassociated with the #1 correlation is not a $50 or $100, the #1correlation is compared to a threshold of 1900 at step 1306. If the #1correlation is less than or equal to 1900, the correlation number is toolow to identify the denomination of the bill with certainty. Therefore,step 1308 sets a "no call" bit in a correlation result flag and thesystem returns to the main program at step 1310. If, however, the #1correlation is greater than 1900 at step 1306, the system advances tostep 1312 which determines whether the #1 correlation is greater than2000. If the #1 correlation is greater than 2000, the correlation numberis sufficiently high that the denomination of the scanned bill can beidentified with certainty without any further checking. Consequently, a"good call" bit is set in the correlation result flag at step 1314 andthe system returns to the main program at step 1310.

If the #1 correlation is not greater than 2000 at step 1312, step 1316checks the denomination associated with the #2 correlation. If thedenomination associated with the #2 correlation is not a $50 or $100,the #2 correlation is compared to a threshold of 1900 at step 1318. Ifthe #2 correlation is less than or equal to 1900, the denominationidentified by the #1 correlation is acceptable, and thus the "good call"bit is set in the correlation result flag at step 1314 and the systemreturns to the main program at step 1310. If, however, the #2correlation is greater than 1900 at step 1318, the denomination of thescanned bill cannot be identified with certainty because the #1 and #2correlations are both above 1900 and, yet, are associated with differentdenominations. Accordingly, the "no call" bit is set in the correlationresult flag at step 1308.

If the denomination associated with the #2 correlation is a $50 or $100at step 1316, the #2 correlation is compared to a threshold of 1500 atstep 1320. If the #2 correlation is less than or equal to 1500, thedenomination identified by the #1 correlation is acceptable, and thusthe "good call" bit is set in the correlation result flag at step 1314and the system returns to the main program at step 1310. If, however,the #2 correlation is greater than 1500 at step 1320, the denominationof the scanned bill cannot be identified with certainty. As a result,the "no call" bit is set in the correlation result flag at step 1308.

If the denomination associated with the #1 correlation is a $50 or $100at step 1304, the #1 correlation is compared to a threshold of 1500 atstep 1322. If the #1 correlation is less than or equal to 1500, thedenomination of the scanned bill cannot be identified with certaintyand, therefore, the "no call" bit is set in the correlation result flagat step 1308. If, however, the #1 correlation at step 1322 is greaterthan 1500, the system advances to step 1312 which determines whether the#1 correlation is greater than 2000. If the #1 correlation is greaterthan 2000, the correlation number is sufficiently high that thedenomination of the scanned bill can be identified with certaintywithout any further checking. Consequently, a "good call" bit is set inthe correlation result flag at step 1314 and the system returns to themain program at step 1310.

If the #1 correlation is not greater than 2000 at step 1312, step 1316checks the denomination associated with the #2 correlation. If thedenomination associated with the #2 correlation is not a $50 or $100,the #2 correlation is compared to a threshold of 1900 at step 1318. Ifthe #2 correlation is less than or equal to 1900, the denominationidentified by the #1 correlation is acceptable, and thus the "good call"bit is set in the correlation result flag at step 1314 and the systemreturns to the main program at step 1310. If, however, the #2correlation is greater than 1900 at step 1318, the denomination of thescanned bill cannot be identified with certainty. Accordingly, the "nocall" bit is set in the correlation result flag at step 1308.

If the denomination associated with the #2 correlation is a $50 or $100at step 1316, the #2 correlation is compared to a threshold of 1500 atstep 1320. If the #2 correlation is less than or equal to 1500, thedenomination identified by the #1 correlation is acceptable, and thusthe "good call" bit is set in the correlation result flag at step 1314and the system returns to the main program at step 1310. If, however,the #2 correlation is greater than 1500 at step 1320, the denominationof the scanned bill cannot be identified with certainty. As a result,the "no call" bit is set in the correlation result flag at step 1308 andthe system returns to the main program at step 1310.

Now the use of the triple scanhead arrangement 1200 in scanning anddiscriminating German currency will be described. When scanning Germanbills, only the output of the center scanhead 1202 is utilized togenerate scanned patterns. A segment similar to segment S of FIG. 4 isscanned over the center of the transport path at a predetermineddistance D₆ inboard after the leading edge of a bill is detected. In apreferred embodiment D₆ is 0.25" (0.635 cm). The scanned segmentcomprises 64 samples as shown in FIGS. 3 and 5. In a preferredembodiment German bills are scanned at a rate of 1000 bills per minute.The lateral location of the scanned segment is fixed relative to thetransport path 1216 but may vary left to right relative to bill 1210since the lateral position of bill 1210 may vary left to right withinthe transport path 1216.

FIG. 54a illustrates the general areas scanned in generating master 10DM German patterns. Due to the short length of 10 DM bills in their longdimension relative to the width of the transport path, thirty 10 DMmaster patterns are stored. A first set of five patterns are generatedby scanning a genuine 10 DM bill 1400 in the forward direction alonglaterally displaced segments all beginning a predetermined distance D₆inboard of the leading edge of the bill 1400. Each of these fivelaterally displaced segments is centered about a respective one of linesL₁ -L₅. One such segment S10₁ centered about line L₁ is illustrated inFIG. 54a. Line L₁ is disposed down the center C of the bill 1400. In apreferred embodiment lines L₂ -L₅ are disposed in a symmetrical fashionabout the center C of the bill 1400. In a preferred embodiment lines L₂and L₃ are laterally displaced from L₁ by a distance D₇ where D₇ is0.24" (0.61 cm) and lines L₄ and L₅ are laterally displaced from L₁ by adistance D₈ where D₈ is 0.48" (1.22 cm).

A second set of five patterns are generated by scanning a genuine 10 DMbill 1400 in the forward direction along laterally displaced segmentsalong lines L₁ -L₅ all beginning at a second predetermined distanceinboard of the leading edge of the bill 1400, the second predetermineddistance being less than the predetermined distance D₆. One such segmentS10₂ centered about line L₁ is illustrated in FIG. 54a. In a preferredembodiment the second predetermined distance is such that scanningbegins one sample earlier than D₆, that is about 30 mils before theinitiation of the patterns in the first set of five patterns.

A third set of five patterns are generated by scanning a genuine 10 DMbill 1400 in the forward direction along laterally displaced segmentsalong lines L₁ -L₅ all beginning at a third predetermined distanceinboard of the leading edge of the bill 1400, the third predetermineddistance being greater than the predetermined distance D₆. One suchsegment S10₃ centered about line L₁ is illustrated in FIG. 54a. In apreferred embodiment the third predetermined distance is such thatscanning begins one sample later than D₆, that is about 30 mils afterthe initiation of the patterns in the first set of five patterns.

The above three sets of five patterns yield fifteen patterns in theforward direction. Fifteen additional 10 DM master patterns taken in themanner described above but in the reverse direction are also stored.

FIG. 54b illustrates the general areas scanned in generating master 20DM, 50 DM, and 100 DM German patterns. Due to the lengths of 20 DM, 50DM, and 100 DM bills in their long dimension being shorter than thewidth of the transport path, eighteen 20 DM master patterns, eighteen 50DM master patterns, and eighteen 100 DM master patterns are stored. The50 DM master patterns and the 100 DM master patterns are taken in thesame manner as the 20 DM master patterns except that the 50 DM masterpatterns and 100 DM master patterns are generated from respectivegenuine 50 DM bills and 100 DM bills while the 20 DM master patterns aregenerated from genuine 20 DM bills. Therefore, only the generation ofthe 20 DM master patterns will be described in detail.

A first set of three patterns are generated by scanning a genuine 20 DMbill 1402 in the forward direction along laterally displaced segmentsall beginning a predetermined distance D₆ inboard of the leading edge ofthe bill 1402. Each of these three laterally displaced segments iscentered about a respective one of lines L₆ -L₈. One such segment S20₁centered about line L₆ is illustrated in FIG. 54b. Line L₆ is disposeddown the center C of the bill 1402. In a preferred embodiment lines L₇-L₈ are disposed in a symmetrical fashion about the center C of the bill1402. In a preferred embodiment lines L₇ and L₈ are laterally displacedfrom L₆ by a distance D₉ where D₉ is 0.30" (0.76 cm) for the 20 DM bill.The value of D₉ is 0.20" (0.51 cm) for the 50 DM bill and 0.10" (0.25cm) for the 100 DM bill.

A second set of three patterns are generated by scanning a genuine 20 DMbill 1402 in the forward direction along laterally displaced segmentsalong lines L₆ -L₈ all beginning at a second predetermined distanceinboard of the leading edge of the bill 1402, the second predetermineddistance being less than the predetermined distance D₆. One such segmentS20₂ centered about line L₆ is illustrated in FIG. 54b. In a preferredembodiment the second predetermined distance is such that scanningbegins one sample earlier than D₆, that is about 30 mils before theinitiation of the patterns in the first set of three patterns.

A third set of three patterns are generated by scanning a genuine 20 DMbill 1402 in the forward direction along laterally displaced segmentsalong lines L₆ -L₈ all beginning at a third predetermined distanceinboard of the leading edge of the bill 1402, the third predetermineddistance being greater than the predetermined distance D₆. One suchsegment S20₃ centered about line L₆ is illustrated in FIG. 54b. In apreferred embodiment the third predetermined distance is such thatscanning begins one sample later than D₆, that is about 30 mils afterthe initiation of the patterns in the first set of three patterns.

The above three sets of three patterns yield nine patterns in theforward direction. Nine additional 20 DM master patterns taken in themanner described above but in the reverse direction are also stored.Furthermore, the above stored master patterns are generated either byscanning both a relatively new crisp genuine bill and an older yellowedgenuine bill and averaging the patterns generated from each or,alternatively, by scanning an average looking bill.

This yields a total of 84 German master patterns (30 for 10 DM bills, 18for 20 DM bills, 18 for 50 DM bills, and 18 for 100 DM bills). To reducethe number of master patterns that must compared to a given scannedpattern, the narrow dimension of a scanned bill is measured usingphotosensors 1212 and 1214. After a given bill has been scanned by thecenter scanhead 1202, the generated scanned pattern is correlated onlyagainst certain ones of above described 84 master patterns based on thesize of the narrow dimension of the bill as determined by thephotosensors 1212 and 1214. The narrow dimension of each bill ismeasured independently by photosensors 1212 and 1214 and then averagedto indicate the length of the narrow dimension of a bill. In particular,a first number of encoder pulses occur between the detection of theleading and trailing edges of a bill by the photosensor 1212. Likewise,a second number of encoder pulses occur between the detection of theleading and trailing edges of the bill by the photosensor 1214. Thesefirst and second numbers of encoder pulses are averaged to indicate thelength of the narrow dimension of the bill in terms of encoder pulses.

The photosensors 1212 and 1214 can also determine the degree of skew ofa bill as it passes by the triple scanhead arrangement 1200. By countingthe number of encoder pulses between the time when photosensors 1212 and1214 detect the leading edge of a bill, the degree of skew can bedetermined in terms of encoder pulses. If no or little skew is measured,a generated scanned pattern is only compared to master patternsassociated with genuine bills having the same narrow dimension length.If a relatively large degree of skew is detected, a scanned pattern willbe compared with master patterns associated with genuine bills havingthe next smaller denominational amount than would be indicated by themeasured narrow dimension length.

Table 4 indicates which denominational set of master patterns are chosenfor comparison to the scanned pattern based on the measured narrowdimension length in terms of encoder pulses and the measured degree ofskew in terms of encoder pulses:

                  TABLE 4    ______________________________________    Narrow Dimension                 Degree of Skew in                               Selected Set of Master    Length in Encoder Pulses                 Encoder Pulses                               Patterns    ______________________________________    <1515        Not applicable                               10 DM    ≧1515 and <1550                 ≧175   10 DM    ≧1515 and <1550                 <175          20 DM    ≧1550 and <1585                 ≧300   10 DM    ≧1550 and <1585                 <300          20 DM    ≧1585 and <1620                 ≧200   20 DM    ≧1585 and <1620                 <200          50 DM    ≧1620 and <1655                 ≧300   20 DM    ≧1620 and <1655                 <300          50 DM    ≧1655 and <1690                 ≧150   50 DM    ≧1655 and <1690                 <150          100 DM    ≧1690 and <1725                 ≧300   50 DM    ≧1690 and <1725                 <300          100 DM    ≧1725 Not applicable                               100 DM    ______________________________________

FIG. 55 is a flowchart of the threshold test utilized in calling thedenomination of a German bill. It should be understood that thisthreshold test compares the scanned bill pattern only to the set ofmaster patterns selected in accordance with Table 4. Therefore, theselection made in accordance with Table 4 provides a preliminaryindication as to the denomination of the scanned bill. The thresholdtest in FIG. 55, in effect, serves to confirm or overturn thepreliminary indication given by Table 4.

The threshold test of FIG. 55 begins at step 1324. Step 1326 checks thenarrow dimension length of the scanned bill in terms of encoder pulses.If the narrow dimension length is less than 1515 at step 1326, thepreliminary indication is that the denomination of the scanned bill is a10 DM bill. In order to confirm this preliminary indication, the #1correlation is compared to 550 at step 1328. If the #1 correlation isgreater than 550, the correlation number is sufficiently high toidentify the denomination of the bill as a 10 DM bill. Accordingly, a"good call" bit is set in a correlation result flag at step 1330, andthe system returns to the main program at step 1332. If, however, the #1correlation is less than or equal to 550 at step 1328, the preliminaryindication that the scanned bill is a 10 DM bill is effectivelyoverturned. The system advances to step 1334 which sets a "no call" bitin the correlation result flag.

If step 1326 determines that the narrow dimension length is greater thanor equal to 1515, a correlation threshold of 800 is required to confirmthe preliminary denominational indication provided by Table 4.Therefore, if the #1 correlation is greater than 800 at step 1336, thepreliminary indication provided by Table 4 is confirmed. To confirm thepreliminary indication, the "good call" bit is set in the correlationresult flag. If, however, the #1 correlation is less than or equal to800 at step 1336, the preliminary indication is rejected and the "nocall" bit in the correlation result flag is set at step 1334. The systemthen returns to the main program at step 1332.

FIG. 56 is a functional block diagram illustrating another embodiment ofa currency discriminator system 1662. The discriminator system 1662comprises an input receptacle 1664 for receiving a stack of currencybills. A transport mechanism (as represented by arrows A and B)transports the bills in the input receptacle past an authenticating anddiscriminating unit 1666 to a canister 1668 where the bills arere-stacked. In addition to determining the denomination of each scannedbill, the authenticating and discriminating unit 1666 may additionallyinclude various authenticating tests such as the ultravioletauthentication test described below.

Signals from the authenticating and discriminating unit 1666 are sent toa signal processor such as a central processor unit ("CPU") 1670. TheCPU 1670 records the results of the authenticating and discriminatingtests in a memory 1672. When the authenticating and discriminating unit1666 is able to confirm the genuineness and denomination of a bill, thevalue of the bill is added to a total value counter in memory 1672 thatkeeps track of the total value of the stack of bills that was insertedin the input receptacle 1664 and scanned by the authenticating anddiscriminating unit 1666. Additionally, depending on the mode ofoperation of the discriminator system 1662, counters associated with oneor more denominations are maintained in the memory 1672. For example, a$1 counter may be maintained to record how many $1 bills were scanned bythe authenticating and discriminating unit 1666. Likewise, a $5 countermay be maintained to record how many $5 bills were scanned, and so on.In an operating mode where individual denomination counters aremaintained, the total value of the scanned bills may be determinedwithout maintaining a separate total value counter. The total value ofthe scanned bills and/or the number of each individual denomination maybe displayed on a display 1674 such as a monitor or LCD display.

As discussed above, a discriminating unit such as the authenticating anddiscriminating unit 1666 may not be able to identify the denomination ofone or more bills in the stack of bills loaded into the input receptacle1664. For example, if a bill is excessively worn or soiled or if thebill is torn, a discriminating unit may not be able to identify thebill. Furthermore, some known discrimination methods do not have a highdiscrimination efficiency and thus are unable to identify bills whichvary even somewhat from an "ideal" bill condition or which are evensomewhat displaced by the transport mechanism relative to the scanningmechanism used to discriminate bills. Accordingly, such poorerperforming discriminating units may yield a relatively large number ofbills which are not identified.

The discriminator system 1662 may be designed so that when theauthenticating and discriminating unit is unable to identify a bill, thetransport mechanism is altered to divert the unidentified bill to aseparate storage canister. Such bills may be "flagged" or "marked" toindicate that the bill is a no call or suspect bill. Alternatively, theunidentified bill may be returned to the customer. The discriminatorsystem 1662 may be designed to continue operation automatically when abill is diverted from the normal transport path because the bill is a"no call" or a counterfeit suspect, or the system may be designed torequire a selection element to be depressed. For example, uponexamination of a returned bill the customer may conclude that thereturned bill is genuine even though it was not identified by thediscriminating unit. However, because the bill was not identified, thetotal value and/or denomination counters in the memory 1672 will notreflect its value. Nevertheless, the customer may wish to deposit thebill for subsequent verification by the bank.

Turning now to FIG. 57, there is shown a functional block diagramillustrating another embodiment of a document authenticator anddiscriminator according to the present invention. The discriminatorsystem 1680 comprises an input receptacle 1682 for receiving a stack ofcurrency bills. A transport mechanism (as represented by arrow C)transports the bills from the input receptacle, one at a time, past anauthenticating and discriminating unit 1684. Based on the results of theauthenticating and discriminating unit 1684, a bill is eithertransported to a verified-deposit canister 1686 (arrow D), to an escrowcanister 1688 (arrow E), or to a return station 1690 (arrow F). When isbill is determined to be genuine and its denomination has beenidentified, the bill is transported to the verified-deposit canister1686. Alternatively, where the authenticating and discriminating unitdetermines that a bill is a fake, the bill is immediately routed (arrowE) to the escrow canister 1688. Finally, if a bill is not determined tobe fake but for some reason the authenticating and discriminating unit1684 is not able to identify the denomination of the bill, the flaggedbill is returned (arrow F) to the customer at station 1690. If thecustomer concludes that the bill is genuine, the customer may depositthe returned bill or bills in an envelope for later verification by thebank and crediting to the customer's account. The discriminator system1680 then resumes operation, and the suspect bills in the depositenvelope are held for manual pick-up without incrementing the countersassociated with the various denomination and/or the total valuecounters.

Referring now to FIGS. 58--58, there is shown a document authenticatingsystem using ultraviolet ("UV") light. A UV light source 2102illuminates a document 2104. Depending upon the characteristics of thedocument, ultraviolet light may be reflected off the document and/orfluorescent light may be emitted from the document. A detection system2106 is positioned so as to receive any light reflected or emittedtoward it but not to receive any UV light directly from the light source2102. The detection system 2106 comprises a UV sensor 2108, afluorescence sensor 2110, filters, and a plastic housing. The lightsource 2102 and the detection system 2106 are both mounted to a printedcircuit board 2112. The document 2104 is transported in the directionindicated by arrow A by a transport system (not shown). The document istransported over a transport plate 2114 which has a rectangular opening2116 in it to permit passage of light to and from the document. In apreferred embodiment, the rectangular opening 2116 is 1.375 inches(3.493 cm) by 0.375 inches (0.953 cm). To minimize dust accumulationonto the light source 2102 and the detection system 2106 and to preventdocument jams, the opening 2116 is covered with a transparentUV-transmitting acrylic window 2118. To further reduce dustaccumulation, the UV light source 2102 and the detection system 2106 arecompletely enclosed within a housing (not shown) comprising thetransport plate 2114.

Referring now to FIG. 59, there is shown a functional block diagramillustrating a preferred embodiment of a UV authenticating system. FIG.59 shows a UV sensor 2202, a fluorescence sensor 2204, and filters 2206,2208 of a detection system such as the detection system 2106 of FIG. 59.Light from the document passes through the filters 2206, 2208 beforestriking the sensors 2202, 2204, respectively. An ultraviolet filter2206 filters out visible light and permits UV light to be transmittedand hence to strike the UV sensor 2202. Similarly, a visible lightfilter 2208 filters out UV light and permits visible light to betransmitted and hence to strike fluorescence sensor 2204. Accordingly,UV light, which has a wavelength below 400 nm, is prevented fromstriking the fluorescence sensor 2204, and visible light, which has awavelength greater than 400 nm, is prevented from striking the UV sensor2202. In a preferred embodiment the UV filter 2206 transmits lighthaving a wavelength between about 260 nm and about 380 nm and has a peaktransmittance at 360 nm. In a preferred embodiment, the visible lightfilter 2208 is a blue filter and preferably transmits light having awavelength between about 415 nm and about 620 nm and has a peaktransmittance at 450 nm. The preferred blue filter comprises acombination of a blue component filter and a yellow component filter.The blue component filter transmits light having a wavelength betweenabout 320 nm and about 620 nm and has a peak transmittance at 450 nm.The yellow component filter transmits light having a wavelength betweenabout 415 nm and about 2800 nm. Examples of suitable filters are UG1 (UVfilter), BG23 (blue bandpass filter), and GG420 (yellow longpassfilter), all manufactured by Schott.

The UV sensor 2202 outputs an analog signal proportional to the amountof light incident thereon, and this signal is amplified by amplifier2210 and fed to a microcontroller 2212. Similarly, the fluorescencesensor 2204 outputs an analog signal proportional to the amount of lightincident thereon and this signal is amplified by amplifier 2214 and fedto a microcontroller 2212. Analog-to-digital converters 2216 within themicrocontroller 2212 convert the signals from the amplifiers 2210, 2214to digital and these digital signals are processed by the software ofthe microcontroller 2212. The UV sensor 2202 may be, for example, anultraviolet enhanced photodiode sensitive to light having a wavelengthof about 360 nm and the fluorescence sensor 2204 may be a blue enhancedphotodiode sensitive to light having a wavelength of about 450 nm. Suchphotodiodes are available from, for example, Advanced Photonix, Inc.,Massachusetts. The microcontroller 2212 may be, for example, a Motorola68HC16.

The exact characteristics of the sensors 2202, 2204 and the filters2206, 2208 including the wavelength transmittance ranges of the abovefilters are not as critical as the prevention of the fluorescence sensorfrom generating an output signal in response to ultraviolet light, andthe prevention of the ultraviolet sensor from generating an outputsignal in response to visible light. For example, instead of, or inaddition to, filters, the authentication system may employ anultraviolet sensor which is not responsive to light having a wavelengthlonger than 400 nm and/or a fluorescence sensor which is not responsiveto light having a wavelength shorter than 400 nm.

Calibration potentiometers 2218, 2220 permit the gains of amplifiers2210, 2214 to be adjusted to appropriate levels. Calibration may beperformed by positioning a piece of white fluorescent paper on thetransport plate 2114 so that it completely covers the rectangularopening 2116. The potentiometers 2218, 2220 may then be adjusted so thatthe output of the amplifiers 2210, 2214 is 5 volts.

It has been determined that genuine United States currency reflects ahigh level of ultraviolet light and does not fluoresce under ultravioletillumination. It has also been determined that under ultravioletillumination counterfeit United States currency exhibits one of the foursets of characteristics listed below:

1) Reflects a low level of ultraviolet light and fluoresces;

2) Reflects a low level of ultraviolet light and does not fluoresce;

3) Reflects a high level of ultraviolet light and fluoresces;

4) Reflects a high level of ultraviolet light and does not fluoresce.

Counterfeit bills in categories (1) and (2) may be detected by acurrency authenticator employing an ultraviolet light reflection test.Counterfeit bills in category (3) may be detected by a currencyauthenticator employing both an ultraviolet reflection test and afluorescence test. Only counterfeits in category (4) are not detected bythe authenticating methods of the present invention.

Fluorescence is determined by any signal that is above the noise floor.Thus, the amplified fluorescent sensor signal 2222 will be approximately0 volts for genuine U.S. currency and will vary between approximately 0and 5 volts for counterfeit bills, depending upon their fluorescencecharacteristics. Accordingly, an authenticating system will reject billswhen signal 2222 exceeds approximately 0 volts.

A high level of reflected UV light ("high UV") is indicated when theamplified UV sensor signal 2224 is above a predetermined threshold. Thehigh/low UV threshold is a function of lamp intensity and reflectance.Lamp intensity can degrade by as much as 50% over the life of the lampand can be further attenuated by dust accumulation on the lamp and thesensors. The problem of dust accumulation is mitigated by enclosing thelamp and sensors in a housing as discussed above. The authenticatingsystem tracks the intensity of the UV light source and readjusts thehigh/low threshold accordingly. The degradation of the UV light sourcemay be compensated for by periodically feeding a genuine bill into thesystem, sampling the output of the UV sensor, and adjusting thethreshold accordingly. Alternatively, degradation may be compensated forby periodically sampling the output of the UV sensor when no bill ispresent in the rectangular opening 2116 of the transport plate 2114. Itis noted that a certain amount of UV light is always reflected off theacrylic window 2118. By periodically sampling the output of the UVsensor when no bill is present, the system can compensate for lightsource degradation. Furthermore, such sampling can also be used toindicate when the ultraviolet light source has burned out or otherwiserequires replacement. This may be accomplished, for example, by means ofa display reading or an illuminated light emitting diode ("LED"). Theamplified ultraviolet sensor signal 2224 will initially vary between 1.0and 5.0 volts depending upon the UV reflectance characteristics of thedocument being scanned and will slowly drift downward as the lightsource degrades. Alternatively, the sampling of the UV sensor output maybe used to adjust the gain of the amplifier 2210, thereby maintainingthe output of the amplifier 2210 at its initial levels.

It has been found that the voltage ratio between counterfeit and genuineU.S. bills varies from a discernable 2-to-1 ratio to a non-discernableratio. Thus, a 2-to-1 ratio is used to discriminate between genuine andcounterfeit bills. For example, if a genuine U.S. bill generates anamplified UV output sensor signal 2224 of 4.0 volts, documentsgenerating an amplified UV output sensor signal 2224 of 2.0 volts orless will be rejected as counterfeit. As described above, this thresholdof 2.0 volts may either be lowered as the light source degrades or thegain of the amplifier 2210 may be adjusted so that 2.0 volts remains anappropriate threshold value.

The determination of whether the level of UV reflected off a document ishigh or low is made by sampling the output of the UV sensor at a numberof intervals, averaging the readings, and comparing the average levelwith the predetermined high/low threshold. Alternatively, a comparisonmay be made by measuring the amount of UV light reflected at a number oflocations on the bill and comparing these measurements with thoseobtained from genuine bills. Alternatively, the output of one or more UVsensors may be processed to generate one or more patterns of reflectedUV light and these patterns may be compared to the patterns generated bygenuine bills.

In a similar manner, the presence of fluorescence may be determined bysampling the output of the fluorescence sensor at a number of intervals.However, a bill is rejected as counterfeit U.S. currency if any of thesampled outputs rise above the noise floor. The alternative methodsdiscussed above with respect to processing the signal or signals of a UVsensor or sensors may also be employed, especially with respect tocurrencies of other countries or other types of documents which mayemploy as security features certain locations or patterns of fluorescentmaterials.

FIGS. 60-63 illustrate a disc-type coin sorter that uses a coin-drivingmember having a resilient surface for moving coins along a metalcoin-guiding surface of a stationary coin-guiding member. Thecoin-driving member is a rotating disc, and the coin-guiding member is astationary sorting head. As can be seen in FIG. 60, a hopper 1510receives coins of mixed denominations and feeds them through centralopenings in a housing 1511 and a coin-guiding member in the form of anannular sorting head or guide plate 1512 inside or underneath thehousing. As the coins pass through these openings, they are deposited onthe top surface of a coin-driving member in the form of a rotatable disc1513. This disc 1513 is mounted for rotation on a stub shaft (not shown)and driven by an electric motor 1514 mounted to a base plate 1515. Thedisc 1513 comprises a resilient pad 1516 bonded to the top surface of asolid metal disc 1517.

The top surface of the resilient pad 1516 is preferably spaced from thelower surface of the sorting head 1512 by a gap of about 0.005 inches(0.13 mm). The gap is set around the circumference of the sorting head1512 by a three point mounting arrangement including a pair of rearpivots 1518, 1519 loaded by respective torsion springs 1520 which tendto elevate the forward portion of the sorting head. During normaloperation, however, the forward portion of the sorting head 1512 is heldin position by a latch 1522 which is pivotally mounted to the frame 1515by a bolt 1523. The latch 1522 engages a pin 1524 secured to the sortinghead. For gaining access to the opposing surfaces of the resilient pad1516 and the sorting head, the latch is pivoted to disengage the pin1524, and the forward portion of the sorting head is raised to an upwardposition (not shown) by the torsion springs 1520.

As the disc 1513 is rotated, the coins 1525 deposited on the top surfacethereof tend to slide outwardly over the surface of the pad due tocentrifugal force. The coins 1525, for example, are initially displacedfrom the center of the disc 1513 by a cone 1526, and therefore aresubjected to sufficient centrifugal force to overcome their staticfriction with the upper surface of the disc. As the coins moveoutwardly, those coins which are lying flat on the pad enter the gapbetween the pad surface and the guide plate 1512 because the undersideof the inner periphery of this plate is spaced above the pad 16 by adistance which is about the same as the thickness of the thickest coin.As further described below, the coins are sorted into their respectivedenominations, and the coins for each denomination issue from arespective exit slot, such as the slots 1527, 1528, 1529, 1530, 1531 and1532 (see FIGS. 60 and 61) for dimes, pennies, nickels, quarters,dollars, and half-dollars, respectively. In general, the coins for anygiven currency are sorted by the variation in diameter for the variousdenominations.

Preferably most of the aligning, referencing, sorting, and ejectingoperations are performed when the coins are pressed into engagement withthe lower surface of the sorting head 1512. In other words, the distancebetween the lower surfaces of the sorting head 1512 with the passagesconveying the coins and the upper surface of the rotating disc 1513 isless than the thickness of the coins being conveyed. As mentioned above,such positive control permits the coin sorter to be quickly stopped bybraking the rotation of the disc 1513 when a preselected number of coinsof a selected denomination have been ejected from the sorter. Positivecontrol also permits the sorter to be relatively compact yet operate athigh speed. The positive control, for example, permits the single filestream of coins to be relatively dense, and ensures that each coin inthis stream can be directed to a respective exit slot.

Turning now to FIG. 61, there is shown a bottom view of the preferredsorting head 1512 including various channels and other means especiallydesigned for high-speed sorting with positive control of the coins, yetavoiding the galling problem. It should be kept in mind that thecirculation of the coins, which is clockwise in FIG. 60, appearscounterclockwise in FIG. 61 because FIG. 61 is a bottom view. Thevarious means operating upon the circulating coins include an entranceregion 1540, means 1541 for stripping "shingled" coins, means 1542 forselecting thick coins, first means 1544 for recirculating coins, firstreferencing means 1545 including means 1546 for recirculating coins,second referencing means 1547, and the exit means 1527, 1528, 1529,1530, 1531 and 1532 for six different coin denominations, such as dimes,pennies, nickels, quarters, dollars and half-dollars. The lowermostsurface of the sorting head 1512 is indicated by the reference numeral1550.

Considering first the entrance region 1540, the outwardly moving coinsinitially enter under a semi-annular region underneath a planar surface1561 formed in the underside of the guide plate or sorting head 1512.Coin C1, superimposed on the bottom plan view of the guide plate in FIG.61 is an example of a coin which has entered the entrance region 1540.Free radial movement of the coins within the entrance region 1540 isterminated when they engage a wall 1562, though the coins continue tomove circumferentially along the wall 1562 by the rotational movement ofthe pad 1516, as indicated by the central arrow in the counterclockwisedirection in FIG. 61. To prevent the entrance region 1540 from becomingblocked by shingled coins, the planar region 1561 is provided with aninclined surface 1541 forming a wall or step 1563 for engaging the uppermost coin in a shingled pair. In FIG. 61, for example, an upper coin C2is shingled over a lower coin C3. As further shown in FIG. 62, movementof the upper coin C2 is limited by the wall 1563 so that the upper coinC2 is forced off of the lower coin C3 as the lower coin is moved by therotating disc 1513.

Returning to FIG. 61, the circulating coins in the entrance region 1540,such as the coin C1, are next directed to the means 1542 for selectingthick coins. This means 1542 includes a surface 1564 recessed into thesorting head 1512 at a depth of 0.070 inches (1.78 mm) from thelowermost surface 1550 of the sorting head. Therefore, a step or wall1565 is formed between the surface 1561 of the entrance region 1540 andthe surface 1564. The distance between the surface 1564 and the uppersurface of the disc 1513 is therefore about 0.075 inches so thatrelatively thick coins between the surface 1564 and the disc 1513 areheld by pad pressure. To initially engage such thick coins, an initialportion of the surface 1564 is formed with a ramp 1566 located adjacentto the wall 1562. Therefore, as the disc 1513 rotates, thick coins inthe entrance region that are next to the wall 1562 are engaged by theramp 1566 and thereafter their radial position is fixed by pressurebetween the disc and the surface 1564. Thick coins which fail toinitially engage the ramp 1566, however, engage the wall 1565 and aretherefore recirculated back within the central region of the sortinghead. This is illustrated, for example, in FIG. 63 for the coin C4. Thisinitial selecting and positioning of the thick coins prevents misalignedthick coins from hindering the flow of coins to the first referencingmeans 1545.

Returning now to FIG. 61, the ramp 1566 in the means 1542 for selectingthe thick coins can also engage a pair or stack of thin coins. Such astack or pair of thin coins will be carried under pad pressure betweenthe surface 1564 and the rotating disc 1513. In the same manner as athick coin, such a pair of stacked coins will have its radial positionfixed and will be carried toward the first referencing means 1545. Thefirst means 1545 for referencing the coins obtains a single-file streamof coins directed against the outer wall 1562 and leading up to a ramp1573.

Coins are introduced into the referencing means 1545 by the thinnercoins moving radially outward via centrifugal force, or by the thickercoin(s) C52a following concentricity via pad pressure. The stacked coinsC58a and C50a are separated at the inner wall 1582 such that the lowercoin C58a is carried against surface 1572a. The progression of the lowercoin C58a is depicted by its positions at C58b, C58c, C58d, and C58e.More specifically, the lower coin C58 becomes engaged between therotating disc 1513 and the surface 1572 in order to carry the lower cointo the first recirculating means 1544, where it is recirculated by thewall 1575 at positions C58d and C58e. At the beginning of the wall 1582,a ramp 1590 is used to recycle coins not fully between the outer andinner walls 1562 and 1582 and under the sorting head 1512. As shown inFIG. 61, no other means is needed to provide a proper introduction ofthe coins into the referencing means 1545.

The referencing means 1545 is further recessed over a region 1591 ofsufficient length to allow the coins C54 of the widest denomination tomove to the outer wall 1562 by centrifugal force. This allows coins C54of the widest denomination to move freely into the referencing means1545 toward its outer wall 1562 without being pressed between theresilient pad 1516 and the sorting head 1512 at the ramp 1590. The innerwall 1582 is preferably constructed to follow the contour of the recessceiling. The region 1591 of the referencing recess 1545 is raised intothe head 1512 by ramps 1593 and 1594, and the consistent contour at theinner wall 1582 is provided by a ramp 1595.

The first referencing means 1545 is sufficiently deep to allow coins C50having a lesser thickness to be guided along the outer wall 1562 bycentrifugal force, but sufficiently shallow to permit coins C52, C54having a greater thickness to be pressed between the pad 1516 and thesorting head 1512, so that they are guided along the inner wall 1582 asthey move through the referencing means 1545. The referencing recess1545 includes a section 1596 which bends such that coins C52, which aresufficiently thick to be guided by the inner wall 1582 but have a widthwhich is less than the width of the referencing recess 1545, are carriedaway from the inner wall 1582 from a maximum radial location 1583 on theinner wall toward the ramp 1573.

This configuration in the sorting head 1512 allows the coins of alldenominations to converge at a narrow ramped finger 1573a on the ramp1573, with coins C54 having the largest width being carried between theinner and outer walls via the surface 1596 to the ramped finger 1573a soas to bring the outer edges of all coins to a generally common radiallocation. By directing the coins C50 radially inward along the latterportion of the outer wall 1562, the probability of coins being offsetfrom the outer wall 1562 by adjacent coins and being led onto the rampedfinger 1573a is significantly reduced. Any coins C50 which are slightlyoffset from the outer wall 1562 while being led onto the ramp finger1573a may be accommodated by moving the edge 1551 of exit slot 1527radially inward, enough to increase the width of the slot 1527 tocapture offset coins C50 but to prevent the capture of coins of thelarger denominations. For sorting Dutch coins, the width of the rampfinger 1573a may be about 0.140 inch. At the terminal end of the ramp1573, the coins become firmly pressed into the pad 16 and are carriedforward to the second referencing means 1547.

A coin such as the coin C50c will be carried forward to the secondreferencing means 1547 so long as a portion of the coin is engaged bythe narrow ramped finger 1573a on the ramp 1573. If a coin is notsufficiently close to the wall 1562 so as to be engaged by this rampedfinger 1573a, then the coin strikes a wall 1574 defined by the secondrecirculating means 1546, and that coin is recirculated back to theentrance region 1540.

The first recirculating means 1544, the second recirculating means 1546and the second referencing means 1547 are defined at successivepositions in the sorting head 1512. It should be apparent that the firstrecirculating means 1544, as well as the second recirculating means1546, recirculate the coins under positive control of pad pressure. Thesecond referencing means 1547 also uses positive control of the coins toalign the outer most edge of the coins with a gaging wall 1577. For thispurpose, the second referencing means 1547 includes a surface 1576, forexample, at 0.110 inches (1.27 mm) from the bottom surface of thesorting head 1512, and a ramp 1578 which engages the inner edge portionsof the coins, such as the coin C50d.

As best shown in FIG. 61, the initial portion of the gaging wall 1577 isalong a spiral path with respect to the center of the sorting head 1512and the sorting disc 1513, so that as the coins are positively driven inthe circumferential direction by the rotating disc 1513, the outer edgesof the coins engage the gaging wall 1577 and are forced slightlyradially inward to a precise gaging radius, as shown for the coin C16 inFIG. 62. FIG. 62 further shows a coin C17 having been ejected from thesecond recirculating means 1546.

Referring back to FIG. 61, the second referencing means 1547 terminateswith a slight ramp 1580 causing the coins to be firmly pressed into thepad 1516 on the rotating disc with their outer most edges aligned withthe gaging radius provided by the gaging wall 1577. At the terminal endof the ramp 1580 the coins are gripped between the guide plate 1512 andthe resilient pad 1516 with the maximum compressive force. This ensuresthat the coins are held securely in the new radial position determinedby the wall 1577 of the second referencing means 1547.

The sorting head 1512 further includes sorting means comprising a seriesof ejection recesses 1527, 1528, 1529, 1530, 1531 and 1532 spacedcircumferentially around the outer periphery of the plate, with theinnermost edges of successive slots located progressively farther awayfrom the common radial location of the outer edges of all the coins forreceiving and ejecting coins in order of increasing diameter. The widthof each ejection recess is slightly larger than the diameter of the cointo be received and ejected by that particular recess, and the surface ofthe guide plate adjacent the radially outer edge of each ejection recesspresses the outer portions of the coins received by that recess into theresilient pad so that the inner edges of those coins are tilted upwardlyinto the recess. The ejection recesses extend outwardly to the peripheryof the guide plate so that the inner edges of these recesses guide thetilted coins outwardly and eventually eject those coins from between theguide plate 1512 and the resilient pad 1516.

The innermost edges of the ejection recesses are positioned so that theinner edge of a coin of only one particular denomination can enter eachrecess; the coins of all other remaining denominations extend inwardlybeyond the innermost edge of that particular recess so that the inneredges of those coins cannot enter the recess.

For example, the first ejection recess 1527 is intended to dischargeonly dimes, and thus the innermost edge 1551 of this recess is locatedat a radius that is spaced inwardly from the radius of the gaging wall1577 by a distance that is only slightly greater than the diameter of adime. Consequently, only dimes can enter the recess 1527. Because theouter edges of all denominations of coins are located at the same radialposition when they leave the second referencing means 1547, the inneredges of the pennies, nickels, quarters, dollars and half dollars allextend inwardly beyond the innermost edge of the recess 1527, therebypreventing these coins from entering that particular recess.

At recess 1528, the inner edges of only pennies are located close enoughto the periphery of the sorting head 1512 to enter the recess. The inneredges of all the larger coins extend inwardly beyond the innermost edge1552 of the recess 1528 so that they remain gripped between the guideplate and the resilient pad. Consequently, all the coins except thepennies continue to be rotated past the recess 1528.

Similarly, only nickels enter the ejection recess 1529, only thequarters enter the recess 1530, only the dollars enter the recess 1531,and only the half dollars enter the recess 1532.

Because each coin is gripped between the sorting head 1512 and theresilient pad 16 throughout its movement through the ejection recess,the coins are under positive control at all times. Thus, any coin can bestopped at any point along the length of its ejection recess, even whenthe coin is already partially projecting beyond the outer periphery ofthe guide plate. Consequently, no matter when the rotating disc isstopped (e.g., in response to the counting of a preselected number ofcoins of a particular denomination), those coins which are alreadywithin the various ejection recesses can be retained within the sortinghead until the disc is re-started for the next counting operation.

One of six proximity sensors S₁ -S₆ is mounted along the outboard edgeof each of the six exit channels 1527-1532 in the sorting head forsensing and counting coins passing through the respective exit channels.By locating the sensors S₁ -S₆ in the exit channels, each sensor isdedicated to one particular denomination of coin, and thus it is notnecessary to process the sensor output signals to determine the coindenomination. The effective fields of the sensors S₁ -S₆ are all locatedjust outboard of the radius at which the outer edges of all coindenominations are gaged before they reach the exit channels 1527-1532,so that each sensor detects only the coins which enter its exit channeland does not detect the coins which bypass that exit channel. Only thelargest coin denomination (e.g., U.S. half dollars) reaches the sixthexit channel 1532, and thus the location of the sensor in this exitchannel is not as critical as in the other exit channels 1527-1531.

In addition to the proximity sensors S1-S6, each of the exit channels1527-1532 also includes one of six coin discrimination sensors D1-D6.These sensors D1-D6 are the eddy current sensors, and will be describedin more detail below in connection with FIGS. 64-67 of the drawings.

When one of the discrimination sensors detects a coin material that isnot the proper material for coins in that exit channel, the disc may bestopped by de-energizing or disengaging the drive motor and energizing abrake. The suspect coin may then be discharged by jogging the drivemotor with one or more electrical pulses until the trailing edge of thesuspect coin clears the exit edge of its exit channel. The exact discmovement required to move the trailing edge of a coin from its sensor tothe exit edge of its exit channel, can be empirically determined foreach coin denomination and then stored in the memory of the controlsystem. An encoder on the sorter disc can then be used to measure theactual disc movement following the sensing of the suspect coin, so thatthe disc can be stopped at the precise position where the suspect coinclears the exit edge of its exit channel, thereby ensuring that no coinsfollowing the suspect coin are discharged.

Turning now to FIGS. 64-67, one embodiment of the present inventionemploys an eddy current sensor 1710 to perform as the coin handlingsystem's coin discrimination sensors D1-D6. The eddy current sensor 1710includes an excitation coil 1712 for generating an alternating magneticfield used to induce eddy currents in a coin 1714. The excitation coil1712 has a start end 1716 and a finish end 1718. An embodiment an a-c.excitation coil voltage V_(ex), e.g., a sinusoidal signal of 250 KHz and10 volts peak-to-peak, is applied across the start end 1716 and thefinish end 1718 of the excitation coil 1712. The alternating voltageV_(ex) produces a corresponding current in the excitation coil 1712which in turn produces a corresponding alternating magnetic field. Thealternating magnetic field exists within and around the excitation coil1712 and extends outwardly to the coin 1714. The magnetic fieldpenetrates the coin 1714 as the coin is moving in close proximity to theexcitation coil 1712, and eddy currents are induced in the coin 1714 asthe coin moves through the alternating magnetic field. The strength ofthe eddy currents flowing in the coin 1714 is dependent on the materialcomposition of the coin, and particularly the electrical resistance ofthat material. Resistance affects how much current will flow in the coin1614 according to Ohm's Law (voltage=current*resistance).

The eddy currents themselves also produce a corresponding magneticfield. A proximal detector coil 1722 and a distal coil 1724 are disposedabove the coin 1714 so that the eddy current-generated magnetic fieldinduces voltages upon the coils 1722, 1724. The distal detector coil1724 is positioned above the coin 1714, and the proximal detector coil1722 is positioned between the distal detector coil 1724 and the passingcoin 1714.

In one embodiment, the excitation coil 1712, the proximal detector coil1722 and the distal detector coil 1724 are all wound in the samedirection (either clockwise or counterclockwise). The proximal detectioncoil 1722 and the distal detector coil 1724 are wound in the samedirection so that the voltages induced on these coils by the eddycurrents are properly oriented.

The proximal detection coil 1722 has a starting end 1726 and a finishend 1728. Similarly, the distal coil 1724 has a starting end 1730 and afinish end 1632. In order of increasing distance from the coin 1614, thedetector coils 1722, 1724 are positioned as follows: finish end 1728 ofthe proximal detector coil 1722, start end 1726 of the proximal detectorcoil 1722, finish end 1732 of the distal detector coil 1724 and startend 1730 of the distal detector coil 1724. The finish end 1728 of theproximal detection coil 1722 is connected to the finish end 1732 of thedistal detector coil 1724 via a conductive wire 1734. It will beappreciated by those skilled in the art that other detector coil 1722,1724 combinations are possible. For example, in an alternativeembodiment the proximal detection coil 1722 is wound in the oppositedirection of the distal detection coil 1724. In this case the start end1726 of the proximal coil 1722 is connected to the finish end 1732 ofthe distal coil 1724.

Eddy currents in the coin 1714 induce voltages V_(prox) and V_(dist)respectively on the detector coils 1722, 1724. Likewise, the excitationcoil 1712 also induces a common-mode voltage V_(com) on each of thedetector coils 1722, 1724. The common-mode voltage V_(com) iseffectively the same on each detector coil due to the symmetry of thedetector coils' physical arrangement within the excitation coil 1712.Because the detector coils 1722, 1724 are wound and physically orientedin the same direction and connected at their finish ends 1728, 1732, thecommon-mode voltage V_(com) induced by the excitation coil 1712 issubtracted out, leaving only a difference voltage V_(diff) correspondingto the eddy currents in the coin 1714. This eliminates the need foradditional circuitry to subtract out the common-mode voltage V_(com).The common-mode voltage V_(com) is effectively subtracted out becauseboth the distal detection coil 1724 and the proximal detection coil 1722receive the same level of induced voltage V_(com) from the excitationcoil 1712.

Unlike the common-mode voltage, the voltages induced by the eddy currentin the detector coils are not effectively the same. This is because theproximal detector coil 1722 is purposely positioned closer to thepassing coin than the distal detector coil 1724. Thus, the voltageinduced in the proximal detector coil 1722 is significantly stronger,i.e. has greater amplitude, than the voltage induced in the distaldetector coil 1724. Although the present invention subtracts the eddycurrent-induced voltage on the distal coil 1724 from the eddycurrent-induced voltage on the proximal coil 1722, the voltage amplitudedifference is sufficiently great to permit detailed resolution of theeddy current response.

As seen in FIG. 64, the excitation coil 1712 is radially surrounded by amagnetic shield 1734. The magnet shield 1734 has a high level ofmagnetic permeability in order to help contain the magnetic fieldsurrounding the excitation coil 1712. The magnetic shield 1734 has theadvantage of preventing stray magnetic field from interfering with othernearby eddy current sensors. The magnetic shield is itself radiallysurrounded by a steel outer case 1736.

In one embodiment the excitation coil utilizes a cylindrical ceramic(e.g., alumina) core 1738. Alumina has the advantages of beingimpervious to humidity and providing a good wear surface. It isdesirable that the core 1748 be able to withstand wear because it maycome into frictional contact with the coin 1714. Alumina withstandsfrictional contact well because of its high degree of hardness, i.e.,approximately 9 on mohs scale.

To form the eddy current sensor 1510, the detection coils 1722, 1724 arewound on a coil form (not shown). A preferred form is a cylinder havinga length of 0.5 inch, a maximum diameter of 0.2620 inch, a minimumdiameter of 0.1660 inch, and two grooves of 0.060 inch width spacedapart by 0.060 inch and spaced from one end of the form by 0.03 inch.Both the proximal detection coil 1722 and the distal detector coil 1724have 350 turns of #44 AWG enamel covered magnet wire layer wound togenerally uniformly fill the available space in the grooves. Each of thedetector coils 1722, 1724 are wound in the same direction with thefinish ends 1728, 1732 being connected together by the conductive wire1734. The start ends 1726, 1730 of the detector coils 1722, 1724 areconnected to separately identified wires in a connecting cable.

The excitation coil 1712 is a generally uniformly layer wound on acylindrical alumina ceramic coil form having a length of 0.5 inch, anoutside diameter of 0.2750 inch, and a wall thickness of 0.03125 inch.The excitation coil 1712 is wound with 135 turns of #42 AWG enamelcovered magnet wire in the same direction as the detector coils 1722,1724. The excitation coil voltage V_(ex) is applied across the start end1716 and the finish end 1718.

After the excitation coil 1712 and detector coils 1722, 1724 are wound,the excitation coil 1712 is slipped over the detector coils 1722, 1724around a common center axis. At this time the sensor 1710 is connectedto a test oscillator (not shown) which applies the excitation voltageV_(ex) to the excitation coil 1712. The excitation coil's position isadjusted along the axis of the coil to give a null response from thedetector coils 1722, 1724 on an a-c. voltmeter with no metal near thecoil windings.

Then the magnetic shield 1644 is the slipped over the excitation coil1712 and adjusted to again give a null response from the detector coils1722, 1724.

The magnetic shield 1744 and coils 1712, 1722, 1724 within the magneticshield 1744 are then placed in the steel outer case 1746 andencapsulated with a polymer resin (not shown) to "freeze" the positionof the magnetic shield 1744 and coils 1712, 1722, 1724.

After curing the resin, an end of the eddy current sensor 1710 nearestthe proximal detector coil 1722 is sanded and lapped to produce a flatand smooth surface with the coils 1712, 1722 slightly recessed withinthe resin.

In order to detect the effect of the coin 1714 on the voltages inducedupon the detector coils 1722, 1724, it is preferred to use a combinationof phase and amplitude analysis of the detected voltage. This type ofanalysis minimizes the effects of variations in coin surface geometryand in the distance between the coin and the coils.

The voltage applied to the excitation coil 1712 causes current to flowin the coil 1712 which lags behind the voltage 1720. For example, thecurrent may lag the voltage 1720 by 90 degrees in a superconductivecoil. In effect, the coin's 1714 eddy currents impose a resistive losson the current in the excitation coil 1712. Therefore, the initial phasedifference between the voltage and current in the excitation coil 1712is decreased by the presence of the coin 1714. Thus, when the detectorcoils 1724, 1726 have a voltage induced upon them, the phase differencebetween the voltage applied to the excitation coil 1712 and that of thedetector coils is reduced due to the eddy current effect in the coin.The amount of reduction in the phase difference is proportional to theelectrical and magnetic characteristics of the coin and thus thecomposition of the coin. By analyzing both the phase difference and themaximum amplitude, an accurate assessment of the composition of the coinis achieved.

FIGS. 67A and 67B illustrate a preferred phase-sensitive detector 1750for sampling the differential output signal V_(diff) from the twodetector coils 1722, 1724. The differential output signal V_(diff) ispassed through a buffer amplifier 252 to a switch 1754, where thebuffered V_(diff) is sampled once per cycle by momentarily closing theswitch 1754. The switch 1754 is controlled by a series of referencepulses produced from the V_(ex) signal, one pulse per cycle. Thereference pulses 1758 are synchronized with excitation voltage V_(ex),so that the amplitude of the differential output signal V_(diff) duringthe sampling interval is a function not only of the amplitude of thedetector coil voltages 1736, 1738, but also of the phase differencebetween the signals in excitation coil 1712 and the detection coils1736, 1738.

The pulses derived from V_(ex) are delayed by an "offset angle" whichcan be adjusted to minimize the sensitivity of V_(diff) to variations inthe gap between the proximal face of the sensor 1710 and the surface ofthe coin 1714 being sensed. The value of the offset angle for any givencoin can be determined empirically by moving a standard metal disc, madeof the same material as the coin 1714, from a position where it contactsthe sensor face, to a position where it is spaced about 0.001 to 0.020inch from the sensor face. The signal sample from the detector 1750 ismeasured at both positions, and the difference between the twomeasurements is noted. This process is repeated at several differentoffset angles to determine the offset angle which produces the minimumdifference between the two measurements.

Each time buffered V_(diff) is sampled, the resulting sample is passedthrough a second buffer amplifier 1756 to an analog-to-digital converter(not shown). The resulting digital value is supplied to a microprocessor(not shown) which compares that value with several different ranges ofvalues stored in a lookup table (not shown). Each stored range of valuescorresponds to a particular coin material, and thus the coin materialrepresented by any given sample value is determined by the particularstored range into which the sample value falls. The stored ranges ofvalues can be determined empirically by simply measuring a batch ofcoins of each denomination and storing the resulting range of valuesmeasured for each denomination.

If desired, the coin sorting and counting module 8 may be replaced witha coin discriminating module which does not sort the coins. Such amodule would align the coins of all denominations in a single file andguide them past a single coin discrimination sensor to determine whetherthe coins are genuine. The coins of all denominations would then bedischarged into a single storage receptacle and sorted at a later time.Coins that are detected to be non-genuine would be diverted and returnedto the customer at the coin return station 4.

When an invalid coin is detected by one of the discriminating sensorsdescribed above, the invalid coin is separated from the valid coins andreturned to the customer. In the illustrative module 8, this separationis effected outside the sorting disc by the shunting device illustratedin FIGS. 68-71. The curved exit chute 1800 includes two slots 1802, 1804separated by an internal partition 1806. The internal partition 1806 ispivotally mounted to a stationary base 1808 so that the internalpartition 1806 may be moved, perpendicular to the plane of the coins, byan actuator 1810 between an up position (FIG. 70) and a down position(FIG. 69). The exit chute 1800 is positioned adjacent an exit channel ofthe coin sorter such that coins exiting the coin sorter are guided intothe slot 1802 when the internal partition 1806 is in the down position(FIG. 69). When an invalid coin is detected by the discriminating sensorD, the actuator 1810 moves the internal partition 1806 to the upposition (FIG. 66) so that the invalid coin now enters the slot 1804 ofthe exit chute 1800. Coins entering the slot 1804 are discharged intothe tube 9 that conveys those coins to the coin-return slot 4 at thefront of the ATM. While FIGS. 67-70 illustrate only a single exit chute,it will be apparent that a similar exit chute is provided at each of thesix coin exit locations around the circumference of the sorting disc.

The actuator 1810 moves the internal partition 1806 between the up anddown positions in response to detection of invalid and valid coins.Thus, if the internal partition 1806 is in the down position and aninvalid coin is detected, the partition 1806 is moved to the up positionso that the invalid coin will be diverted into the slot 1804.

Alternatively, an invalid coin may be separated from the valid coins byuse of inboard actuators in the sorting head, activated by signalsderived from one or more sensors mounted in the sorting head upstream ofthe actuators. Such an arrangement is described in U.S. Pat. No.5,299,977, which is incorporated herein by reference.

We claim:
 1. A cash processing station for receiving and dispensing cashand substantially immediately furnishing an associated accounting systemwith data, including the value of the cash processed, for eachtransaction, said station comprisingmeans for identifying a customerusing said station and activating said station in response to saididentification, a coin sorter for receiving successive batches of coinsof mixed denomination, sorting the coins by denomination, determiningnon-authentic coins, and generating signals representing the number ofcoins of each denomination in each batch of coins that is processed, acoin return slot, coupled to said coin sorter, for returning saiddetected non-authentic coins to said customer, a coin dispenserincluding a coin storage device for dispensing selected number of coinsfrom said coin storage device, a bill dispenser including a bill storagedevice and controllable transport means for dispensing selected numbersof bills from said storage device, a bill receptacle for receivingstacks of bills to be deposited, a bill counter and scanner for rapidlyremoving the bills one at a time from said receptacle and counting thebills while determining the denomination of each bill, said counter andscanner including means for generating data representing thedenomination of each bill, and the number of bills of each denomination,passed through said counter and scanner, a memory for receiving andstoring data representing the number of bills of each denominationpassed through said counter and scanner in each transaction, and datarepresenting the total value of the bills passed through said counterand scanner in each transaction, and control means for transferring datafrom said memory to an associated cash accounting system so that thedeposits and withdrawals executed at said cash processing station areentered in said accounting system substantially immediately after theexecution of said transactions.
 2. The cash processing station of claim1 wherein said counter and scanner and said transport means processbills at a rate in excess of about 350 bills per minute.
 3. The cashprocessing station of claim 1 wherein said means for identifying acustomer includes a magnetic keycard card reader.
 4. The cash processingstation of claim 1 wherein said control means includes a microprocessor.5. The system of claim 1 further including means for dispensing rolledcoin.
 6. The system of claim 1 further including means for dispensingstrapped bills.
 7. A cash processing station for receiving anddispensing cash and substantially immediately furnishing an associatedaccounting system with data, including the value of the cash processed,for each transaction, said station comprisinga magnetic keycard readerfor receiving a magnetic keycard, reading said keycard, and identifyinga customer based upon data on said keycard, said magnetic keycard readeractivating said station in response to said identification of saidcustomer, a keyboard for receiving operating instructions from a user,said operating instructions causing the machine to operate in aplurality of modes, a memory for holding a master primary and secondarybill patterns associated with a denomination of a bill, a coin sorterfor receiving successive batches of coins of mixed denomination, sortingthe coins by denomination, determining non-authentic coins, andgenerating signals representing the number of coins of each denominationin each batch of coins and the total value of coins that are processed,said coin sorter coupled to said memory, a coin return slot, coupled tosaid coin sorter, for returning said detected non-authentic coins tosaid customer, a coin dispenser including a coin storage device fordispensing selected number of coins from said coin storage device, abill dispenser including a bill storage device and controllabletransport means for dispensing selected numbers of bills from saidstorage device, a bill receptacle for receiving stacks of bills to bedeposited, a bill counter and scanner, coupled to said memory, forrapidly removing the bills one at a time from said receptacle, saidcounter and scanner including optical scanhead means for illuminatingeach bill and detecting light reflected from the bill and producingcorresponding electrical signals, and signal processing means forreceiving said electrical signals, determining primary and secondarycharacteristics of said bills from said signals, determining thedenomination of the bill based on a comparison between said sensedprimary characteristic and said master primary pattern, determining theauthenticity of said bills, and determining the number of bills of eachdenomination passed through said counter and scanner, escrow holdingmeans for receiving and holding said bills from said bill counter andscanner, a verified deposit canister for receiving bills from saidescrow holding means, wherein said memory receives and stores datarepresenting the number of coins of each denomination processed, thetotal value of the coins processed, the number of bills of eachdenomination passed through said counter and scanner in eachtransaction, the authenticity of said bills, and data representing thetotal value of the bills passed through said counter and scanner in eachtransaction, a video display for displaying said data representing thetotal value of the coins and bills processed, and control means fortransferring data from said memory to an associated cash accountingsystem so that the deposits and withdrawals executed at said cashprocessing station are entered in said accounting system substantiallyimmediately after a transaction.